Add badge and pin v1 in README.md

Author: rffontenelle

README.md

@@ -1,5 +1,7 @@
 # sphinx-lint-problem-matcher
 
+[![Test workflow status badge](https://github.com/rffontenelle/sphinx-lint-problem-matcher/actions/workflows/test.yml/badge.svg)](https://github.com/rffontenelle/sphinx-lint-problem-matcher/actions/workflows/test.yml)
+
 This action adds a GitHub Action problem matcher that annotates messages
 printed by [sphinx-lint][sphinx-lint], making it easier to spot Sphinx
 syntax errors.
@@ -13,7 +15,7 @@ How it shows up in the summary page of a GitHub Action run:
 Set to use this workflow before running `sphinx-lint`. For instance:
 
 ```yaml
-    - uses: rffontenelle/sphinx-lint-problem-matcher@master
+    - uses: rffontenelle/sphinx-lint-problem-matcher@v1
     - run: sphinx-lint docs/*.rst
 ```