Add a GitHub PR template

[hristog]

This PR proposes the introduction of a PR template, following the same structure as those in dask and distributed.

[jrbourbeau]

We'll probably want to add isort and mypy to this check too. At a certain point it might be worth pointing to ci/code_checks.sh or pre-commit instead

[hristog]

We'll probably want to add isort and mypy to this check too.

I was waiting for the resolution of #813 first, before introducing an isort check here, but now that you've brought it up, I don't see why it couldn't be introduced at the current stage.
Thanks for reminding me about mypy - I'd completely forgotten about it.

At a certain point it might be worth pointing to ci/code_checks.sh or pre-commit instead

Do you mean verbally, or is there some related GitHub magic trick(s)?

[hristog]

I've opted to:

• follow the checks as per https://github.com/dask/dask-ml/blob/main/ci/code_checks.sh (e.g., and not do flake8 dask_ml instead of just flake8);
• split the individual code checks into several lines.

Would be happy to amend the PR accordingly, subject to expressed preferences for alternatives.

[hristog]

Hmm the "CI / docs (pull_request)" failure is new:

Updating 'dask-ml-docs' env from conda env update...
  /usr/share/miniconda3/condabin/conda env update --name dask-ml-docs --file /tmp/environment-patched.yml
  Collecting package metadata (repodata.json): ...working... done
  Solving environment: ...working... failed
  Warning: 
  ResolvePackageNotFound: 
    - python[version='3.6.6.*,3.7.*']

  ResolvePackageNotFound: 
    - python[version='3.6.6.*,3.7.*']

It doesn't seem to me that it's related to the most recent commit pushed to this PR.

[hristog]

I can see the same failure in #813.

@jrbourbeau, could this by any chance be related to dask/distributed#4647 (comment)?

[jrbourbeau]

Ah, thanks for pointing the documentation build errors out -- should be fixed by #815