Document the documentation build requirements (closes #8174) - #8191

Please pull the changes.

@vidursatija thanks for the changes and the PR in general. It's much appreciated. I'll try to find time to confirm that everything builds well tonight.

In the mean, perhaps it would make sense to embed the link to the requirements file. See this reference.

Something like:

The `requirements`_ are as follows:

## yada yada yada

.. _requirements:  https://github.com/matplotlib/matplotlib/blob/master/doc-requirements.txt

@phobson can you re-review?
@vidursatija Do you mind rebasing? I can help you out if you don't how to do it?

How can I rebase it?

@NelleV apporved!

@vidursatija Here is some doc on rebasing. I personally use the “interactive” fashion (git rebase -i), which (I find) gives you a bit more grip on what is done. I am not a heavy git user at all and it served me well up to now. If things go sour, you should find help on the Gitter channel.

I think the problem occurred because I didn't change the branch while solving another PR. I'll still use rebase

@vidursatija sorry it took so long to get back to you.

Though it is better to work in a branch, this is unfortunately not the issue here. Basically, someone else has been editing the same file as you, which means you'll have to update your code base. There are two ways to do this: (1) merging; (2) rebasing. The latter is more complicated (with IMO little to 0 benefit…), but I can walk you through it.

The first step is going to be to update your remote branches. Assuming your github remote is called "origin" and the main matplotlib one is called "matplotlib", you can do this by git fetch matplotlib. This will update the code in the remote branch matplotlib/master.

The second step is the rebasing itself. Rebasing will update your master branch in such a way that your commits come after the ones that have been merged into matplotlib/master.
To do this step, do git rebase matplotlib/master. You'll probably have a conflict in which case you'll have to edit the file with the conflict to choose which lines to keep, and continue on with the rebase: first add the file(s) using git add filename to indicate that you've resolved the conflict, and then continue the rebase with git rebase --continue until the rebase is complete.

You can read more on rebase in our development guidelines: http://matplotlib.org/devel/gitwash/development_workflow.html#rebasing-a-pull-request-pr

I've resolved the conflicts by removing the conflicting lines.

Due to some mistake I deleted the forked repository. I still have to add changes. How can I do it?

@vidursatija Do you still have the local changes on your computer?

I have the file.

Unfortunately, that won't be enough to retrieve the changes you've lost. There is unfortunately no other option to start from scratch.

Okay. I'll close this pull request and start a new one?

closed in favor of #8373