Add GitHub files.

.github/FUNDING.yml

@@ -0,0 +1 @@
+custom: https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=donations%40cthing.com&item_name=gradle-cthing-versioning&currency_code=USD&source=url

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup Java
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '17'
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@v3
+      - name: Run clean build javadoc
+        run: ./gradlew clean build javadoc