ci: check for changes to README and man page

Adds a check to CI on changes to either README.rst or git-secrets.1 that
will fail if changes are made to one but not the other.

Fixes: awslabs#243

Signed-off-by: ginglis13 <ginglis05@gmail.com>

.github/workflows/sync-readme-manpage.yml

@@ -0,0 +1,34 @@
+---
+name: "Sync README and man page"
+
+on:
+  push:
+    branches:
+      - 'master'
+    paths:
+      - 'README.rst'
+      - 'git-secrets.1'
+  pull_request:
+    branches:
+      - 'master'
+    paths:
+      - 'README.rst'
+      - 'git-secrets.1'
+
+jobs:
+  sync-readme-man-page:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - run: |
+      README_CHANGED=$(git diff --exit-code README.rst &>/dev/null; echo $?)
+      MANPAGE_CHANGED=$(git diff --exit-code git-secrets.1 &>/dev/null; echo $?)
+
+      if [[ $README_CHANGE == $MANPAGE_CHANGED ]]; then
+        echo "README and man page in sync."
+        exit 0
+      else
+        echo "If changes are made to one of {README.rst, git-secrets.1}, changes need to be made to the other."
+        exit 1
+      fi
+