Issue #3450211 by immaculatexavier, joachim: Documented in Readme that...

Issue #3450211 by immaculatexavier, joachim: Documented in Readme that CommonMark v1 needs to be used because v2 is not supported yet.

README.md

@@ -26,7 +26,7 @@ the "official" [Drupal Coding Standard](https://www.drupal.org/project/coding_st
     
   - **CommonMark and CommonMark GFM (highly recommended, [league/commonmark](https://github.com/thephpleague/commonmark)):**
     ```
-    composer require league/commonmark
+    composer require league/commonmark ^1
     ```
   - Parsedown ([erusev/parsedown](https://github.com/erusev/parsedown)):
     ```