We might be able to "not" also fork fastai-docs

[richarddwang]

As pointed in #512 by @KushajveerSingh .
We should use absolute path for fastai-docs in .gitmodules, so we need to only fork fastai2.

[submodule "docs"]
	path = docs
	url = https://github.com/fastai/fastai-docs
	branch = master

This is also confirmed by the answers to my question on stackoverflow.
How to set .gitmodules so that contributors don't have to fork also submodule?

It should be worth trying it.

[jph00]

That then forces https mode, but some folks (like me!) want to use ssh.