Website - Add other usecases to the overview page
Website - Add other usecases to the overview page

Add Twitter Manhattan and Herddb.org Distributed Databases usecases for BookKeeper as Write-Ahead-Log

Author: Enrico Olivelli <eolivelli@apache.org>

Reviewers: Sijie Guo <sijie@apache.org>

This closes #1539 from eolivelli/fix/websiteusacase

sijie/bookkeeper,apache/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper