Add instructions for getting make to work on Windows

[barrettj12]

Fixes #633 (kinda)

Please squash and merge into a single commit.

[mortberg]

Lots of minor stylistic comments. I don't have windows so cannot test, but I think it's good to have these instructions in case someone else has problems

[Saizan]

By the way, I don't think INSTALL.md should tell users to use make for agda/cubical, it's not necessary to "install" the library.

In that case if you install Agda through cabal or stack you won't have to run make at all.

[barrettj12]

By the way, I don't think INSTALL.md should tell users to use make for agda/cubical, it's not necessary to "install" the library.

In that case if you install Agda through cabal or stack you won't have to run make at all.

True, it's just to test that the installation worked right? I was thinking you could factor this out into a separate section, since this part seems to be repeated verbatim for each installation method.

[Saizan]

Yeah, make only tests that the installed agda can typecheck all the files of the library.

Btw, I still think it's helpful to know how to get make to work on windows, but probably more for someone contributing so that they can run the tests.

[barrettj12]

@mortberg fixed. @Saizan had a good point that this is not necessary in the INSTALL.md file, so I've reverted this to the current version.

[mortberg]

Looks good to me!