Recommend flutter config --help for an explanation of each feature flag (#12293)

Bubble up that `flutter config --help` explains what each flag controls.

cc @vashworth @matanlurey 

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Author: loic-sharma

src/content/tools/pubspec.md

@@ -85,7 +85,7 @@ dev_dependencies:
 
   [!generate: true!] # Enables generation of localized strings from arb files
 
-  [!config:!] # App-specific configuration flags that mirror flutter config
+  [!config:!] # App-specific configuration flags that mirror `flutter config`
     [!enable-swift-package-manager: true!]
 
   [!assets:!]  # Lists assets, such as image files
@@ -234,9 +234,12 @@ The available keys mirror those available in `flutter config --list`.
 ```yaml title="pubspec.yaml"
 flutter:
   config:
+    cli-animations: false
     enable-swift-package-manager: true
 ```
 
+Use `flutter config --help` for a description of each flag.
+
 Flags are only read from the current _application_ package, and have no effect
 in the context of a package or dependency.