added pd as namespace
- [x ] closes https://github.com/pydata/pandas/pull/12268#discussion_r55924987

This is the msg:
more consistent with code in the rest of the document

added more namespace

Generally, also numpy's randn should used as
np.random.randn

isolated namespace changes

Note:
I hope I got the rebase & merge right.

@dacoex no, @sinhrks is asking if you can make that change. should be straightforward.
 Ah, OK. will do.
 pls build the docs. This makes most things actually fail as there are lots of additional imports that are needed (or `pd.`) pre-pended
 @dacoex can you update
 Sorry, I'd been busy with some other items off the coding domain.
What shall I update?
Reference:
https://github.com/pydata/pandas/pull/12608#issuecomment-204411671
 can you rebase and update
 can you rebase / update?
 pls reopen when you can update
