Add CI badge to README

[PeterTh]

It seemed off to me to have a coverage badge but not a CI badge. Also, we all know that more badges = better project, right?

Also snuck in a minor addition to .gitignore for a different build path pattern.

[github-actions[bot]]

Check-perf-impact results: (4c65f1399a47e0eb1340f63004745b17)

:question: No new benchmark data submitted. :question:
Please re-run the microbenchmarks and include the results if your commit could potentially affect performance.

[coveralls]

Pull Request Test Coverage Report for Build 7724255844

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.856%

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Totals
Change from base Build 7697894673:	0.0%
Covered Lines:	4990
Relevant Lines:	5188

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💛 - Coveralls