proposal: Update supported protocols

[domdomegg]

I've noticed a few protocols are missing from https://ddclient.net/protocols.html that are supported by ddclient.

I intend to add these to the docs, but before I invested too much time into this figured I better check there isn't ongoing work / other stuff for me to be aware of here :)

[LenardHess]

Apologies for the radio silence - no there is no significant effort going on there so far.
I'll be taking a look over #6 and also spend some time myself getting the docs updated - especially the provider details wrt. the migration to dual IPv4 and IPv6 support.