Update README and branding for v1.0 release

Author: Swechhya

README.md

@@ -14,7 +14,7 @@ jobs:
     steps:
     - uses: actions/checkout@v1
     - name: R Build and Checks
-      uses: Swechhya/R-actions@master
+      uses: Swechhya/R-actions@v1.0
       with:
         action: 'all'
 ```

action.yml

@@ -1,5 +1,8 @@
 name: 'R-actions'
 description: 'Automatically build and test your R projects'
+branding:
+  icon: 'check-square'
+  color: 'blue'
 inputs:
   action:  # id of inpu
     description: 'What should be run? One of: ["all", "build"]'