DOC: fix link to offset strings in resample method
 - [ ] closes #xxxx

The link to offset strings was not rendered correctly, I've made a sections ```Notes```, and placed the link there.
Part of issue #14843 
hmm, does this fix the link rendering? can you build locally and see @jreback yes it does!
See attached screencap
![screenshot - 080317 - 19 38 20](https://cloud.githubusercontent.com/assets/10461030/23718204/e115b5a8-0436-11e7-9e9b-beac5dd8d3f2.png)
 @DaanVanHauwermeiren Thanks!