fix(docs): Update readme

Author: coturiv

.github/workflows/ci.yml

@@ -17,6 +17,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v1
+    - uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
     - name: Use coturiv/setup-ionic
       uses: ./
     - name: Run cordova project tests

README.md

@@ -7,6 +7,10 @@ Set up your GitHub Actions workflow with Cordova/Ionic environment. Only support
 ## example usage:
 
 ```
+- name: Use coturiv/setup-ionic
+  uses: coturiv/setup-ionic@v1
+  with:
+    java-version: 8
 - name: Use coturiv/setup-ionic
   uses: coturiv/setup-ionic@v1
   with:
@@ -16,4 +20,15 @@ Set up your GitHub Actions workflow with Cordova/Ionic environment. Only support
   run: |
     ionic cordova build android --prod
 
+```
+
+### important*
+
+_From Ubuntu 20.04 runners, the default version of Java is 11, so you need to specify it to 8(1.8), due to the requirement of cordova, but will be removed in future releases. See [here](), and [here](https://cordova.apache.org/docs/en/latest/guide/platforms/android/index.html#java-development-kit-jdk)_
+
+```
+- name: Set up JDK 1.8
+  uses: actions/setup-java@v1
+  with:
+    java-version: 1.8
 ```