Update docs with info on new link checker tips and limitations

[mrjones-plip]

with the recent link checker feature, we should be sure to document any tips and caveats in the documentation style section

specifically:

Fragment-only links in shortcodes and _index.md files** - Avoid full-path self-references (like [link](/current-page/#heading)) inside {{< tab >}} shortcodes as they cause builds to hang.

[mrjones-plip]

@cliftonmcintosh - feel free to grab this when you get a sec!

[cliftonmcintosh]

@mrjones-plip - I'd be happy to work on this. Can you assign it to me, please?