Add some header-goodies for et. (flutter/engine#51434)

I.e. a "open issues" and "file an issue" link.

---------

Co-authored-by: Loïc Sharma <737941+loic-sharma@users.noreply.github.com>

engine/src/flutter/tools/engine_tool/README.md

@@ -1,9 +1,15 @@
 # The Engine Tool
 
+[![Open `e: engine-tool` issues](https://img.shields.io/github/issues/flutter/flutter/e%3A%20engine-tool)](https://github.com/flutter/flutter/issues?q=is%3Aopen+is%3Aissue+label%3A%22e%3A+engine-tool%22)
+
 This is a command line Dart program that automates workflows in the
 `flutter/engine` repository.
 
-### Prerequisites
+> [!NOTE]
+> This tool is under development and is not yet ready for general use. Consider
+> filing a [feature request](https://github.com/flutter/flutter/issues/new?labels=e:engine-tool,team-engine).
+
+## Prerequisites
 
 The tool requires an initial `gclient sync -D` as described in the [repo setup
 steps](https://github.com/flutter/flutter/wiki/Setting-up-the-Engine-development-environment#getting-the-source)
@@ -13,14 +19,14 @@ before it will work.
 
 The tool has the following commands.
 
-* `help` - Prints helpful information about commands and usage.
-* `build` - Builds the Flutter engine.
-* `fetch` - Downloads Flutter engine dependencies.
-* `format` - Formats files in the engine tree using various off-the-shelf
-formatters.
-* `run` - Runs a flutter application with a local build of the engine.
-* `query builds` - Lists the CI builds described under `ci/builders` that the
-host platform is capable of executing.
+- `help` - Prints helpful information about commands and usage.
+- `build` - Builds the Flutter engine.
+- `fetch` - Downloads Flutter engine dependencies.
+- `format` - Formats files in the engine tree using various off-the-shelf
+  formatters.
+- `run` - Runs a flutter application with a local build of the engine.
+- `query builds` - Lists the CI builds described under `ci/builders` that the
+  host platform is capable of executing.
 
 ### Missing features
 
@@ -28,41 +34,41 @@ There are currently many missing features. Some overall goals are listed in the
 GitHub issue [here](https://github.com/flutter/flutter/issues/132807). Some
 desirable new features would do the following:
 
-* Add a `doctor` command.
-* Update the engine checkout so that engine developers no longer have to remember
-to run `gclient sync -D`.
-* Build and test the engine using CI configurations locally, with the
-possibility to override or add new build options and targets.
-* Build engines using options coming only from the command line.
-* List tests and run them locally, automatically building their dependencies
-first. Automatically start emulators or simulators if they're needed to run a
-test.
-* Spawn individual builders remotely using `led` from `depot_tools`.
-* Encapsulate all code formatters, checkers, linters, etc. for all languages.
-* Find a compatible version of the flutter/flutter repo, check it out, and spawn
-tests from that repo with a locally built engine to run on an emulator,
-simulator or device.
-* Use a real logging package for prettier terminal output.
-* Wire the tool up to a package providing autocomplete like
-[cli_completion](https://pub.dev/packages/cli_completion.).
+- Add a `doctor` command.
+- Update the engine checkout so that engine developers no longer have to remember
+  to run `gclient sync -D`.
+- Build and test the engine using CI configurations locally, with the
+  possibility to override or add new build options and targets.
+- Build engines using options coming only from the command line.
+- List tests and run them locally, automatically building their dependencies
+  first. Automatically start emulators or simulators if they're needed to run a
+  test.
+- Spawn individual builders remotely using `led` from `depot_tools`.
+- Encapsulate all code formatters, checkers, linters, etc. for all languages.
+- Find a compatible version of the flutter/flutter repo, check it out, and spawn
+  tests from that repo with a locally built engine to run on an emulator,
+  simulator or device.
+- Use a real logging package for prettier terminal output.
+- Wire the tool up to a package providing autocomplete like
+  [cli_completion](https://pub.dev/packages/cli_completion.).
 
 The way the current tooling in the engine repo works may need to be rewritten,
 especially tests spawned by `run_tests.py`, in order to provide this interface.
 
 ## Contributing
 
-* Follow the [Flutter style guide](https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo)
-for Dart code that are relevant outside of the framework repo. It contains
-conventions that go beyond code formatting, which
-we'll follow even if using `dart format` in the future.
-* Do not call directly into `dart:io` except from `main.dart`. Instead access
-the system only through the `Enviroment` object.
-* All commands must have unit tests. If some functionality needs a fake
-implementation, then write a fake implementation.
-* When adding or changing functionality, update this README.md file.
-* *Begin with the end in mind* - Start working from what the interface provided
-by this tool *should* be, then modify underlying scripts and tools to provide
-APIs to support that.
+- Follow the [Flutter style guide](https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo)
+  for Dart code that are relevant outside of the framework repo. It contains
+  conventions that go beyond code formatting, which
+  we'll follow even if using `dart format` in the future.
+- Do not call directly into `dart:io` except from `main.dart`. Instead access
+  the system only through the `Enviroment` object.
+- All commands must have unit tests. If some functionality needs a fake
+  implementation, then write a fake implementation.
+- When adding or changing functionality, update this README.md file.
+- _Begin with the end in mind_ - Start working from what the interface provided
+  by this tool _should_ be, then modify underlying scripts and tools to provide
+  APIs to support that.
 
 Run tests using `//flutter/testing/run_tests.py`: