Add screenshot for "Profile Readmes" to docs (go-gitea#28964)

introduced in go-gitea#23260 ... the docs still looks to empty:
https://docs.gitea.com/usage/profile-readme

this changes it :)

Author: 6543

docs/content/usage/profile-readme.en-us.md

@@ -19,3 +19,7 @@ To display a Markdown file in your Gitea user or organization profile page, crea
 Gitea will automatically display the contents of the file on your profile, in a new "Overview" above your repositories.
 
 Making the `.profile` repository private will hide the Profile README.
+
+Example of user with `.profile/README.md`:
+
+![profile readme screenshot](./profile-readme.png)