How to add a public key?

[jgithubrecht]

I'm trying to replace my "broken" Twitter key and/or create a new public key. I don't understand how to do so! Here is the message I get when I try to do it in my browser at keybase.io:

• When I run the command "keybase pgp gen" in Terminal, I get this error message: zsh: command not found: keybase
• So what do I need to do?
• Aargh!