Improve branch selection in launch process

[kakoga]

Is your feature request related to a problem? Please describe.
When a user launches a site step 1 asks them to enter a domain, however there is no instruction/indication for what the dropdown does and it allows users to add a domain without selecting a branch.

Describe the solution you'd like
Instead of -None- it would be helpful to instruct the user to Select a Branch & not allow the user to click the 'add domain' button unless a branch has been selected.

Describe alternatives you've considered
Add a note to documentation explaining what the dropdown is used for. However, I know that not all users will look at the documentation therefore it would be better to have that instruction in the UI (in addition to the docs).

Additional context
side note: I think the spacing in the dropdown could be tightened too.