Document what to do if dependencies have changed

[ctrueden]

Apologies if I'm filing this issue in the wrong place.

I maintain a couple of packages on conda-forge, and with a recent release of one of them, the dependencies changed. The bot filed a PR in response to the release on PyPI, and generated this summary block:

It is very likely that the current package version for this feedstock is out of date.
Notes and instructions for merging this PR:

1. Please check that the dependencies have not changed.
2. Please merge the PR only after the tests have passed.
3. Feel free to push to the bot's branch to update this PR if needed.
4. The bot will almost always only open one PR per version.

If this PR was opened in error or needs to be updated please add the bot-rerun label to this PR. The bot will close this PR and schedule another one.

Followed by the small print explaining that cf-regro-autotick-bot is what filed the PR, and pointing to this issue tracker to discuss any concerns. So here I am. 😄

The CI failed because the dependencies had in fact changed: there was a new dependency on psutil. However, based on the explanation above, I did not know how to address this, and ranted a little in the comments.

I think the bot should be adjusted to:

1. Link to relevant documentation about how to define conda-forge dependencies, and/or mention the recipe/meta.yaml file;
2. Link to relevant documentation (which I could not find) about the bot-rerun tag, and/or explain in a little more detail the circumstances where you might want to add that label.

Thoughts?

[djsutherland]

Related: #22. It would definitely be good to add a sentence about what to do when requirements have changed, though.

It also might be a good idea for the bot (or recipes, somehow, since the bot doesn't actually build...) to run pip check to verify that requirements are satisfied. Should we be automatically adding this as a test to python packages or something?

[CJ-Wright]

Would it be worth writing a piggy back migrator that adds pip check as a test command to all feedstocks that depend on pip?

[beckermr]

The pip check migrator is done now.