Add simple placeholderd for each of the CLI functions.

[johnnymatthews]

Simply to speed up the creation of docs in the feat/pre-testnet-launch branch, let's add some simple placeholder stuff to the CLI page just to give basic explanations for what each function does. It'd be nice to throw in what the CLI shows as well, but that's not 100% mandatory. Similar to:

## Balance

Get the balance of an account. You can select any of the accounts stored locally, or enter an Entropy address.

```shell
? Choose account: (Use arrow keys)
  aragon (5FTwtSAjnKFybzkAKvyEo7owikXcHXmwzN7MzjwDNKEbjkub)
> charlie (5Ck5SLSHYac6WFt5UZRSsdJjwmpSZq85fd5TRNAdZQVzEAPT)
  Other

[johnnymatthews]

Closed by #45.