Add reference link comment for Prettier filename matching patterns

Prettier uses filename pattern matching to identify the programming language of files (and from this determines which
files to format, and how to format those files). This is based on data from the "Linguist" project.

That data was used as a reference for configuring the paths filter of the "Check Prettier Formatting" workflow, which
ensures that the workflow will run whenever relevant files are modified.

Documenting that reference via a comment in the workflow will facilitate the maintenance of the paths filter.

Author: per1234

.github/workflows/check-prettier-formatting-task.yml

@@ -11,6 +11,8 @@ on:
       - "**/.npmrc"
       - "**/.prettierignore"
       - "**/.prettierrc*"
+      # Prettier-covered file patterns are defined by:
+      # https://github.com/github-linguist/linguist/blob/main/lib/linguist/languages.yml
       # CSS
       - "**.css"
       - "**.wxss"