Suggest compileOnlyApi rather than compile for AutoValue with Gra…

…dle.

Since `compileOnlyApi` is a recent feature, continue to mention the old way in a note.

Fixes #995.

RELNOTES=n/a
PiperOrigin-RevId: 362995141

value/userguide/index.md

@@ -149,14 +149,15 @@ Gradle users can declare the dependencies in their `build.gradle` script:
 
 ```groovy
 dependencies {
-  // Use 'api' rather than 'compile' for Android or java-library projects.
-  compile             "com.google.auto.value:auto-value-annotations:${autoValueVersion}"
+  compileOnlyApi      "com.google.auto.value:auto-value-annotations:${autoValueVersion}"
   annotationProcessor "com.google.auto.value:auto-value:${autoValueVersion}"
 }
 ```
 
-Note: If you are using a version of Gradle prior to 4.6, you must apply an
-annotation processing plugin [as described in these instructions][tbroyer-apt].
+Note: If you are using a version of Gradle prior to 6.7, use `compile` or (for
+Android or java-library projects) `api` instead of `compileOnlyApi`. If you are
+using a version prior to 4.6, you must apply an annotation processing plugin
+[as described in these instructions][tbroyer-apt].
 
 [tbroyer-apt]: https://plugins.gradle.org/plugin/net.ltgt.apt