Added github actions (#18)

Co-authored-by: Jiawen Geng <technicalcute@gmail.com>

.github/workflows/github-ci.yml

+name: Github Actions
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container: reactnativecommunity/react-native-android
+    steps:
+    - uses: actions/checkout@v2
+    - name: Envinfo
+      run: npx envinfo
+    - name: Build application
+      run: yarn install && cd android && chmod +x gradlew && ./gradlew assembleRelease

README.md

@@ -3,7 +3,7 @@
 [![pipeline status](https://gitlab.com/gengjiawen/ci-sample/badges/master/pipeline.svg)](https://gitlab.com/gengjiawen/ci-sample/commits/master)
 [![Build Status](https://travis-ci.com/react-native-community/ci-sample.svg?branch=master)](https://travis-ci.com/react-native-community/ci-sample)
 [![Build Status](https://dev.azure.com/gengjiawen/open-source/_apis/build/status/react-native-ci-sample/react-native-ci-sample?branchName=master)](https://dev.azure.com/gengjiawen/open-source/_build/latest?definitionId=3?branchName=master)
-
+![Github Actions](https://github.com/thejoaov/ci-sample/workflows/Github%20Actions/badge.svg)
 ## Motivation
 Showcase for using ci to build react native app.
 
@@ -14,3 +14,4 @@ Docker related repo: https://github.com/react-native-community/docker-android.
 * gitlab
 * travis-ci
 * azure devops
+* github actions