Added sample replication hook to "Repl Hook Guide"
Incorporated Edits
Linked riak_object and corrected send_realtime/2

Added version dependent links to the source of riak_object. Corrected
the narrative for send_realtime/2 to include the information about
returning a list to "pre-replicate" objects that the current object
might depend on.
Merge pull request #530 from angrycub/cv_repl_hook_sample

Added sample replication hook to "Repl Hook Guide"