DOC: fix template substitution in pad/bfill docstrings
- [ ] closes #39640
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

#39640 Added doc tag above ffill() to substitute klass
cc @simonjayhawkins @jorisvandenbossche 

lgtm. yeah I can do that. I'm not sure what "Igtm" or "L6516" mean/referring to, if I need to know then could someone let me know please. 

 @dylanp-git lgtm means 'looks good to me'; L6516 is line number 6516
 > @dylanp-git lgtm means 'looks good to me'; L6516 is line number 6516

aha thankyou, I'm slowly learning the lingo!! Thanks a lot @dylanp-git ! > Thanks a lot @dylanp-git !

No worries! I was going to look into it again later as only 20/22 checks passed?

On another note, how many "good first issue" issues do you think I should do before trying something a bit more in-depth? > only 20/22 checks passed?

the failures were unrelated (sometimes that happens)

> how many "good first issue" issues do you think I should do before trying something a bit more in-depth?

IMO if you've got familiar with the contribution workflow then you could start immediately