DOC: Update the pandas.Series.str.find() (Delhi)
Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

- [x] PR title is "DOC: update the pandas.Series.str.find docstring"
- [x] The validation script passes: `scripts/validate_docstrings.py pandas.Series.str.find`
- [x] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] The html version looks good: `python doc/make.py --single pandas.Series.str.find`
- [x] It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

```
################################################################################
###################### Docstring (pandas.Series.str.find) ######################
################################################################################

Retrieve least index of substring.

Return lowest indexes in each strings in the Series/Index
where the substring is fully contained between [start:end].
Return -1 on failure. Equivalent to standard :meth:`str.find`.

Parameters
----------
sub : str
    Substring being searched.
start : int
    Left edge index.
end : int
    Right edge index.

Returns
-------
found : Series/Index of integer values

Examples
--------
>>> s = pd.Series('Finding with pandas')
>>> s.str.find('wi')
0    8
dtype: int64

Returns -1 if the substring is not found in S

>>> s.str.find('wi', start=0, end=5)
0   -1
dtype: int64

See Also
--------
rfind : Return highest indexes in each strings

################################################################################
################################## Validation ##################################
################################################################################
```

If the validation script still gives errors, but you think there is a good reason
to deviate in this case (and there are certainly such cases), please state this
explicitly.


Checklist for other PRs (remove this part if you are doing a PR for the pandas documentation sprint):

- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20153?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@281ce99`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20153/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/20153?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #20153   +/-   ##
=========================================
  Coverage          ?   91.72%           
=========================================
  Files             ?      150           
  Lines             ?    49152           
  Branches          ?        0           
=========================================
  Hits              ?    45086           
  Misses            ?     4066           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.11% <ø> (?)` | |
| #single | `41.84% <ø> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20153?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/20153/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.32% <ø> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20153?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20153?src=pr&el=footer). Last update [281ce99...81c52d4](https://codecov.io/gh/pandas-dev/pandas/pull/20153?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @ChiragSehra! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 13, 2018 at 18:37 Hours UTC Regarding the discussion on gitter: can you add an example with `Series.str.rfind` as well? closing as stale. if you'd like to continue pls ping.