DOC: Add examples for pandas.tseries.timedeltas
Copied examples from the reStructuredText [tutorial](http://pandas.pydata.org/pandas-docs/stable/timedeltas.html) on timedeltas.

@proinsias Thanks a lot for working on examples in docstrings!

Besides the inline comments, another general: maybe it would be nice to have some text between the different examples to somehow put them a bit into context, eg:

```
Parsing a single string to a Timedelta:

>>> ...
>>> ...

Parsing a list or array of strings:

>>> ...

Converting numbers by specifying the `unit` keyword argument:

>>> ...

```
 Thanks for the advice! – I've made these changes and re-pushed the branch. 
 thanks!
