fix: add text language to fenced code block (MD040)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pftg

README.md

@@ -55,7 +55,7 @@ bundle exec rake test
 ```
 
 After Step 1, you'll see:
-```
+```text
 doc/screenshots/
   homepage.png          <- your baseline (commit this)
 ```