DOC: fix ES01 for pandas.plotting.autocorrelation_plot
fixes

```
pandas.plotting.autocorrelation_plot ES01
```

This includes a crisp extended summary of the method which talks about what it does, how it does it and whats the value of it. 

Thanks @tuhinsharma121  > lgtm, but I'm not so familiar with autocorrelation plots, I'll let someone else merge. @Dr-Irv maybe you know about this more?

Not my area at all!