DOC: Add example of skipcols in read_csv
Illustrate how we can use the `usecols` argument to skip particular columns.

Closes #10882.
## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/15052?src=pr) is 84.75% (diff: 100%)
> Merging [#15052](https://codecov.io/gh/pandas-dev/pandas/pull/15052?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will not change coverage

```diff
@@             master     #15052   diff @@
==========================================
  Files           145        145          
  Lines         51146      51146          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          43351      43351          
  Misses         7795       7795          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [018414e...ea3279f](https://codecov.io/gh/pandas-dev/pandas/compare/018414e704670d2d727b9624089caae6f7d12ff1...ea3279fef0d35475f4b256a0745a0b8e38bfcfc2?src=pr) @gfyoung Thanks!