Include markdown files for testing.

Co-authored-by: Michael Park <[email protected]>

.github/workflows/periodic-style-checks.yml

@@ -14,9 +14,9 @@ jobs:
             working-directory: .
     steps:
       - uses: actions/checkout@v4
-      - name: Run vale on .rst files        
+      - name: Run vale on RST and MD files        
         run: |
-          make vale TARGET=*.rst > vale_results.txt
+          make vale TARGET="*.rst *.md" > vale_results.txt
           sed -e 's/\x1b\[[0-9;]*m//g' vale_results.txt > vale_results_clean.txt
 
       - name: Upload artifact