Error in help page of 'trading_md'

[jfgomezok]

Describe the bug
In the help page of trading_md function, the argument symbol has a link that is not working.

To Reproduce
Steps to reproduce the behavior:

1. Go to '?trading_md'
2. Click on 'primary_instruments' link
3. See error: 'No help found for topic primary_instruments in any package.'

Expected behavior
A link to the help page of the 'trading_instruments' function.