Added a gitignore

[claudiouzelac]

This pull request adds a .gitignore file to prevent accidental check-in of Bazel created directories and files.

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This change is 

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
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[ckennelly]

Thanks for the pull request.

Before we can merge it, you'll need to sign our CLA.

[claudiouzelac]

Done.

Thanks for the pull request.

Before we can merge it, you'll need to sign our CLA.

[ckennelly]

@googlebot rescan

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.