[NEW] documentation : cmds not part of redis

[raphaelauv]

The problem/use-case that the feature addresses

the documentation do not explictit the cmds not part of redis

like hrename

Description of the feature

A documentation page of cmds in keyDB not part of redis

[benschermel]

I agree, this is a good idea to consolidate list in one place. We will work on this. Transferring the issue to our documentation repo

[raphaelauv]

we listed all the keydb cmds -> alisaifee/coredis#54