fix(docs): gradle compile config depreciation (#528)

PR facebook/react-native#20767 bumped the version of the Android
Gradle Plugin to v3 which uses the newer Gradle dependency
configurations `implementation` and `api` which make `compile`
obsolete.

PR facebook/react-native#20853 covered the `link` command.

Using `compile` will result in a warning message during app build and
`compile` will be eventually removed by Gradle.

README.md

@@ -102,8 +102,8 @@ Run your project (Cmd+R)
 ```diff
 dependencies {
     ...
-    compile "com.facebook.react:react-native:+"  // From node_modules
-+   compile project(':react-native-device-info')
+    implementation "com.facebook.react:react-native:+"  // From node_modules
++   implementation project(':react-native-device-info')
 }
 ```