Added consistent pandas imports in io documentation
Partially addresses #9886

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14097?src=pr) is 85.26% (diff: 100%)

> Merging [#14097](https://codecov.io/gh/pydata/pandas/pull/14097?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #14097   diff @@
==========================================
  Files           139        139          
  Lines         50490      50502    +12   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43053      43063    +10   
- Misses         7437       7439     +2   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [670435a...4a9f041](https://codecov.io/gh/pydata/pandas/compare/670435ab346d6b35e65b3b1de2b56d850ff25cc6...4a9f041f9b85c75e7095cbd80980f7da95d0b5bc?src=pr)
 @jackieleng Thanks a lot!
