Pip: Installation via `get-pip.py` can be made single line in docs

I am not sure if pipe is available on Windows Command Prompt, for which this instruction applies as well.

Also this solution might not be extensible in other cases, e.g. when we want to invoke get-pip.py with options

Also, I think that piping the download direct to Python encourages people to execute unreviewed code direct from the web, which maybe isn't what we want.

It is, generally, considered best practice to avoid / not suggest users to do curl | sh.

There are a lot of opinion pieces about this topic, on the Internet. While I'm not going to attempt to provide a summary of the various arguments here, here's one of the pieces talking about the pitfalls of recommending curl | sh. The security concerns, the correctness concerns and more are relevant to get-pip.py, and as Paul pointed out, we don't want users to get used to doing things this way.

I'm going to go ahead and close this issue now, since this has been discussed in the past (I can't find the issue/PR where this was discussed last, at the moment). Thanks @saytosid for filing this issue! ^.^