Create README.md

README.md

+# gitlab-ci-android
+This Docker image contains the Android SDK and most common packages necessary for building Android apps in a CI tool like GitLab CI. Make sure your CI environment's caching works as expected, this greatly improves the build time, especially if you use multiple build jobs.
+
+A `.gitlab-ci.yml` with caching of your project's dependencies would look like this:
+
+```
+image: jangrewe/gitlab-ci-android
+
+stages:
+- build
+
+before_script:
+- export GRADLE_USER_HOME=$(pwd)/.gradle
+- chmod +x ./gradlew
+
+cache:
+  key: ${CI_PROJECT_ID}
+  paths:
+  - .gradle/
+    
+build:
+  script:
+  - ./gradlew assembleDebug
+  artifacts:
+    paths:
+    - app/build/outputs/apk/app-debug.apk
+```