Fix documentation about pip being installed by default for Python 2.7.9

[ustun]

• Pip version:
• Python version: 2.7.11
• Operating System: Linux

Description:

The documentation on installation says the following:

pip is already installed if you're using Python 2 >=2.7.9 or Python 3 >=3.4
downloaded from `python.org <https://www.python.org>`_, but you'll need to
:ref:`upgrade pip <Upgrading pip>`.

However, I believe this is wrong since the default configuration for ensurepip is "no".

./configure --help | less

tells me this:

  --with(out)-ensurepip=[=OPTION]
                          "install" or "upgrade" using bundled pip, default is
                          "no"

What I've run:

We should probably put a warning for those people installing from source that pip has to be manually activated before installation.

[dstufft]

@ustun Maybe it needs to be reworded differently, it should be installed by default for people downloading the Windows/OS X isntallers from www.python.org-- but not building from source.

[pfmoore]

I've just clarified this - "pip is already installed if you're using Python 2 >=2.7.9 or Python 3 >=3.4
binaries downloaded..."

[ustun]

Thanks.

Maybe we should add the following as the last paragraph in the first section:

If you are building from source, you need to enable installation of pip via the configure flag by specifying `--with-ensurepip=install`

[dstufft]

With the rewording that Paul added I'm going to go ahead and close this issue. Documentation about building Python should likely go in the Python documentation, but we'd happily to consider PRs that add additional clarification. However I don't believe a tracking issue adds much value.