Update docs for change in the format of snapshot versions.

See #7657.

Author: cpovirk

index.md

@@ -66,8 +66,8 @@ consult the
 ## Snapshots and Documentation
 
 Snapshots of Guava built from the `master` branch are available through Maven
-using version `HEAD-jre-SNAPSHOT`, or `HEAD-android-SNAPSHOT` for the Android
-flavor.
+using version `1.0-HEAD-jre-SNAPSHOT`, or `1.0-HEAD-android-SNAPSHOT` for the
+Android flavor.
 
 [Snapshot API Javadoc][guava-snapshot-api-docs] as well as
 [Snapshot API Diffs][guava-snapshot-api-diffs] are also available.