Change reviewer mention to use {{login}} placeholder

Updated reviewer mention in step 3 documentation.

Author: arilivigni

.github/steps/3-step.md

@@ -100,7 +100,7 @@ In the same Copilot Space conversation do the following:
  > - The improvements should address gaps or inefficiencies identified in the project management documentation.
  > - The pull request should include updates to existing docs or new templates/checklists as needed.
  > - All documents should be in the `docs/` folder
- > - Add me as a reviewer
+ > - Add {{login}} as a reviewer
  > ```
 
 Select **Allow**