Issue description

ch03 missing primary use cases and pro's/Con's for both RGW and MCG.

My suggestions for RGW primary use cases and pro's/con's
Primary use case.
1. When hybrid S3 endpoints is not required.
2. When massive scalability is important.
3. When SPoF isn't allowed.
4. When performance is important.

Pro's
1. Up to 10x better performance, compared with similar resourced NooBaa implementation
2. Massively scalable
3. No inherent SPoF in the design
4. Allows multi-cluster replication (RGW Multisite) between independent Ceph Clusters.
5. Maximum number of objects in an indexed bucket is 65.521*100.000 = ~6.5*10^9 objects
6. Indexless buckets have not hard upper limit, for number of objects.

Con's
1. Endpoint to Endpoint replication requires RGW in both ends.
2. RGW is part of the Ceph package, and therefore requires a ceph storage.