docs(cli): document what --unstable means for cdk gc (#32013)

Minor updates to how `cdk gc` is presented in docs, specifically with regards to the `--unstable` flag.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: kaizencc

packages/aws-cdk/README.md

@@ -895,7 +895,10 @@ cdk bootstrap --no-previous-parameters
 CDK Garbage Collection.
 
 > [!CAUTION]
-> CDK Garbage Collection is under development and therefore must be opted in via the `--unstable` flag: `cdk gc --unstable=gc`.
+> CDK Garbage Collection is under development and therefore must be opted in via the 
+>`--unstable` flag: `cdk gc --unstable=gc`. `--unstable` indicates that the scope and 
+> API of feature might still change. Otherwise the feature is generally production 
+> ready and fully supported.
 
 `cdk gc` garbage collects unused assets from your bootstrap bucket via the following mechanism: 
 

packages/aws-cdk/lib/cli.ts

@@ -115,7 +115,7 @@ async function parseCommandLineArguments(args: string[]) {
       .option('template', { type: 'string', requiresArg: true, desc: 'Use the template from the given file instead of the built-in one (use --show-template to obtain an example)' })
       .option('previous-parameters', { type: 'boolean', default: true, desc: 'Use previous values for existing parameters (you must specify all parameters on every deployment if this is disabled)' }),
     )
-    .command('gc [ENVIRONMENTS..]', 'Garbage collect assets', (yargs: Argv) => yargs
+    .command('gc [ENVIRONMENTS..]', 'Garbage collect assets. Options detailed here: https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk/README.md#cdk-gc', (yargs: Argv) => yargs
       .option('action', { type: 'string', desc: 'The action (or sub-action) you want to perform. Valid entires are "print", "tag", "delete-tagged", "full".', default: 'full' })
       .option('type', { type: 'string', desc: 'Specify either ecr, s3, or all', default: 'all' })
       .option('rollback-buffer-days', { type: 'number', desc: 'Delete assets that have been marked as isolated for this many days', default: 0 })