payload_utils: Add requirements.txt.

- This will be needed to run checker consistently
in different environments (e.g. the python used
by default by Recipes / doesn't have

- Also add common venv name (".venv") to gitignore.

- Steps to create:
  1. Create empty venv: python3 -m venv .venv
  2. Install protobuf: pip install protobuf
  3. Check unittests: python3 -m unittest discover -p *
  4. Write requirements.txt: pip freeze > requirements.txt

TEST=Create venv, install requirements.txt, run unittests.

Change-Id: I81b2e15decd64a99535fb85cdfec0338290fe86f
Tested-by: Andrew Lamb <>
Auto-Submit: Andrew Lamb <>
Commit-Queue: Chris McDonald <>
Reviewed-by: Chris McDonald <>
2 files changed