Use GitHub Actions to publish installer.jar on each push

.github/workflows/ant.yml

@@ -0,0 +1,32 @@
+# Mostly copied from https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-java-with-ant
+# zlatinb
+
+name: Java CI
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up JDK 8
+        uses: actions/setup-java@v2
+        with:
+          java-version: '8'
+          distribution: 'temurin'
+      - name : Generate override.properties
+        run: |
+          rm -f override.properties
+          echo "build.built-by=GitHub Actions" >> override.properties
+          echo "noExe=true" >> override.properties
+      - name: build with Ant
+        run: ant distclean pkg
+      - name: Upload installer.jar
+        uses: actions/upload-artifact@v2
+        with:
+          name: I2P-installer.jar-${{ github.sha }}
+          path: installer.jar
+        
+

README.md

@@ -64,6 +64,9 @@ your `~/.gradle/gradle.properties`:
     systemProp.socksProxyHost=localhost
     systemProp.socksProxyPort=9150
 
+### Development builds
+Automatic CI builds are available at the [continuous integration](https://github.com/i2p/i2p.i2p/actions/workflows/ant.yml) page.
+
 ### Docker
 For more information how to run I2P in Docker, see [Docker.md](Docker.md)
 ## Contact info