Doc: Update example version to 'v1'

Author: BaileyJM02

README.md

@@ -132,7 +132,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - uses: baileyjm02/markdown-to-pdf@master
+      - uses: baileyjm02/markdown-to-pdf@v1
         with:
           input_dir: docs
           output_dir: pdfs