fix: virtual environment to be able to run make test

[nehalmamgain]

The virtual environment expects people can run make test without installing pytest.
This PR fixes issue #104

Before this fix

copying dgp/utils/torch_extension/stn.py -> build/lib/dgp/utils/torch_extension
running egg_info
creating dgp.egg-info
writing dgp.egg-info/PKG-INFO
writing dependency_links to dgp.egg-info/dependency_links.txt
writing entry points to dgp.egg-info/entry_points.txt
writing requirements to dgp.egg-info/requires.txt
writing top-level names to dgp.egg-info/top_level.txt
writing manifest file 'dgp.egg-info/SOURCES.txt'
reading manifest file 'dgp.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
warning: no previously-included files matching '*.proto' found under directory '*'
writing manifest file 'dgp.egg-info/SOURCES.txt'
PYTHONPATH=/home/nehal/dgp: \
pytest -v /home/nehal/dgp/tests/
/bin/sh: 1: pytest: not found
make: *** [Makefile:72: test] Error 127

After this fix

================================================= 56 passed, 3 skipped, 4 warnings in 13.57s ==================================================

---

This change is 

[nehalmamgain]

Link for virtual environment doc
https://github.com/TRI-ML/dgp/blob/master/docs/VIRTUAL_ENV.md

[nehalmamgain]

I got the following error in super linter (even though I didn't touch that comment); so fixing it

/github/workspace/docs/VIRTUAL_ENV.md
  22:208  ✓ error  Incorrect usage of the term: “repo”, use “repository” instead  terminology

✖ 1 problem (1 error, 0 warnings)
✓ 1 fixable problem.

[tk-woven]

Ever since this commit, I think we need to instruct users to pip install -r requirements.txt -r requirements-dev.txt. We can do this in future work, though. This to help others in the meantime. Thank you!

As for the comment issue, usually tools don't lint portions of files but the entire thing, so it looks like that might have been a latent issue since before linting was enabled? Before my time, so not sure. Anyway, much appreciated!

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @nehalmamgain)

[nehalmamgain]

Ever since this commit, I think we need to instruct users to pip install -r requirements.txt -r requirements-dev.txt.

Yup, I agree with you!

As for the comment issue, usually tools don't lint portions of files but the entire thing, so it looks like that might have been a latent issue since before linting was enabled?

Oh, that makes so much sense, thanks!

[nehalmamgain]

Thanks for the merge again!