DOC: minor enhancement of DataFrame.insert docstring
 - [x] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff`` (but not clear to me if I did properly, because the first of the pipe only reports the filename of the changed file, no actual diff.)

My first objective was to clarify the role of `column` vs `value` keyword.

For the reference, this is how this function is documented on http://stackoverflow.com/a/18674915/2822346. Function call is presented as `df.insert(idx, col_name, value)`. I find the `col_name` slightly more explicit than just `column`, which is ambiguous (i.e. "does column holds the Series?"). But of course this name cannot change without breaking the API. So this small PR is just an attempt to clarify things.

Since I was touching the docstring, I've also make it a bit more tidy (e.g. removed a too long line).







The changes look good to me (thanks!), but it seems you have a conflict with master. Can you rebase? Done! It what quite painful for just a few changed lines, but I think it's ok now. I've pulled the latest master. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@539de79`). [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/16341/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #16341   +/-   ##
=========================================
  Coverage          ?   90.37%           
=========================================
  Files             ?      161           
  Lines             ?    50967           
  Branches          ?        0           
=========================================
  Hits              ?    46063           
  Misses            ?     4904           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.15% <ø> (?)` | |
| #single | `40.2% <ø> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.69% <ø> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16341?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/16341?src=pr&el=footer). Last update [539de79...3090f1f](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@539de79`). [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/16341/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #16341   +/-   ##
=========================================
  Coverage          ?   90.37%           
=========================================
  Files             ?      161           
  Lines             ?    50967           
  Branches          ?        0           
=========================================
  Hits              ?    46063           
  Misses            ?     4904           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.15% <ø> (?)` | |
| #single | `40.2% <ø> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.69% <ø> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16341?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/16341?src=pr&el=footer). Last update [539de79...3090f1f](https://codecov.io/gh/pandas-dev/pandas/pull/16341?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @pierre-haessig Thanks!