Revise push-locally instructions

As described in #322882, our instructions on how to push locally do not provide enough information for beginning users. @danielgruesso raised several points, which I'll put here in checkbox format so it's easy to see how this MR is progressing:

1. The command shown in the UI (Create a project from the command line) does not match the documentation. See #322882 - I want an engineer to make a judgment call here, because I can't speak to the merits of one vs the other
2. The "what does this command do?" link takes user to docs that don't actually explain what the command does. Agreed; I can add in some more explanation about what the command does, but we need to settle issue 1 first.
3. For new users, instructing them to push via SSH has pre-reqs, this is not stated in the docs - Cross-link added.
4. For new users, instructing them to push via HTTPS requires them to know their namespace, docs don't indicate how to obtain it - Ouch, yeah, I need to figure out how they know this. What a basic, basic gap...
5. We didn't explain that the text contained placeholders. - This revision fixes that.
6. Add section on how to create projects on a group vs personal namespace Haven't yet tackled.

What this MR does

• Changes a narrative into a set of numbered procedures.
• Cross-links to SSH prerequisites.
• Makes clearer that the user must alter the commands, and how.

Related issues

Related to #322882