update help text in the BTCLI

[dougsillars]

I fixed 3 sections:

1. setting weighst is done by root validators - not senators (all senators are root valis, but not all root valis are senators)
2. registering to root was using the same text as neuron registrtaion for the other subnets. Made this more root specific.
3. removed the wallet name example. this resolves btcli root list-delegates help: implies the ability to filter by wallet, yet not an option #138

[rajkaramchedu]

Good catches, thanks!