Minor cleanups stemming from v0.3.11 release.

[freakboy3742]

The v0.3.11 release highlighted a couple of minor problems.

1. The push instructions for the detached branch weren't quite right
2. The gitignore file for the repo doesn't ignore logs directories.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[mhsmith]

What would create a logs directory that isn't already ignored by one of the other rules? I tried running the unit tests, but they didn't do it.

[freakboy3742]

I did a manual build of the verify-toga app, to replicate one of the failures I saw during the release process. That generated a logs folder in tests/apps.

[mhsmith]

But the tests/apps subdirectories are already ignored by the line above.

[freakboy3742]

Yes, but the logs folder was generated in test/apps, because it was briefcase new that failed, rather than create etc. I guess we could narrow it to that specific known failure; but I figured we might as well have a blanked rule to avoid any stray logs folders.