Improve pip download documentation

It is currently very light and some parts (most of its options) could certainly be factorized with pip wheel and pip install.

[pradyunsg]

I’ve reviewed this today, as part of working on #9475, and this looks good to me! I don’t think factoring out common options is particularly useful; and any additional information/explanations should likely end up in one of the dedicated pages we’re building for the concepts as part of #9475.

[gutsytechster]

@brainwane sure!

The issue says that a lot of options described for pip download can be refactored with options with pip wheel or pip install.

However, when a person would go to the pip download’s documentation, s/he would look for all the available options. So, shouldn’t these options be available for each command’s doc individually?

Apart from that, if you’d compare, the documentation of pip wheeland pip install, there are options between them which exist for each documentation page separately. To list a few of them - --no-clean, --pre, --build, etc.

So, what I feel that current documentation for pip download looks good to me(after looking for other command’s doc).