Updated docstring for copy() method

[agartland]

• closes Copy method does not make truly deep copies of dtype object arrays #12663

Added note that a copy with deep=True does not copy the data of objects contained in underlying arrays with dtype=object.

[jreback]

change this to something like:

deep also copy the indexes (its not the data that addtionally gets copied; a shallow copy does this).

[agartland]

Actually I think deep=False doesn't copy the data at all:

d = pd.DataFrame(rand(3,3))
c = d.copy(deep=False)
c.loc[0,0] = -9
print d

Seems like deep=False is a view of the data and uses the exact same objects for index and columns,
whereas deep=True is a copy of the data and a copy of the index and columns (except for dtype=object)

[agartland]

I tried to be more explicit in this version. I hope this is helpful.

[jreback]

thanks @agartland