Add all commands to the bot help message

The bot's help message only lists one possible command:

`Type 'follow https://yourexcellentsite.com' into the channel or group`

I discovered that I could use the command `unfollow https://yourexcellentsite.com` to unfollow a site, but then I started wondering if there were other hidden commands I didn't know about.

It would be nice to have a list in the help message of all possible commands, so there's no doubt about what's possible.

Start by locating the bot's help-message text and the handlers for the `follow` and `unfollow` commands. Check whether any other commands are supported, then update the help message so it lists every available command and verify that the displayed examples match the supported behavior.

Written by the indexing model from the issue text.