notify developer if helix-bot (github) is not installed on the project

[tripodsan]

Is your feature request related to a problem? Please describe.
If the github helix-bot is not installed on the repository, the dev gets frustrated when their code is not updated after a commit.

the hlx up command could check and then report an error if the bot is not installed.

[kptdobe]

It could give the url to install the bot (assuming it cannot install it for the dev).

[tripodsan]

It could give the url to install the bot (assuming it cannot install it for the dev).

oh.. right. I didn't even think of trying to automatically install it..... ;-)