DOC: Replace astropy channel with conda-forge - #11111

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@mwcraig , so are we doing this or not? If yes, I'll rebase. If not, I'll just close this PR. Please let me know.

I'm in favor of it -- there is no need to remove the astropy channel (i.e. the old instructions will work for the foreseeable future) but I think this is fine to merge once rebased.

Okay, rebased!

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v4.3.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 b2660f922622c8bc971b55975dbe18ab8e1a83b2

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #11111: DOC: Replace astropy channel with conda-forge'

4. Push to a named branch :

git push YOURFORK v4.3.x:auto-backport-of-pr-11111-on-v4.3.x

5. Create a PR against branch v4.3.x, I would have named this PR:

"Backport PR #11111 on branch v4.3.x (DOC: Replace astropy channel with conda-forge)"

And apply the correct labels and milestones.

Congratulation you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove Still Needs Manual Backport label once the PR gets merged.

If these instruction are inaccurate, feel free to suggest an improvement.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v4.0.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 b2660f922622c8bc971b55975dbe18ab8e1a83b2

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #11111: DOC: Replace astropy channel with conda-forge'

4. Push to a named branch :

git push YOURFORK v4.0.x:auto-backport-of-pr-11111-on-v4.0.x

5. Create a PR against branch v4.0.x, I would have named this PR:

"Backport PR #11111 on branch v4.0.x (DOC: Replace astropy channel with conda-forge)"

And apply the correct labels and milestones.

Congratulation you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove Still Needs Manual Backport label once the PR gets merged.

If these instruction are inaccurate, feel free to suggest an improvement.