doc: invalid tags in documentation

[krishnakumarg1984]

please see |UltiSnips#Anon| and |neosnippet#anonymous|, respectively.

In addition, I recommend that one uses a plugin that automatically generates the tag files as necessary, e.g. |gutentags| [1].

I also find |gutentags| [2] to be very convenient for automatically generating and updating tag files.

These tags do not seem to work when trying to follow them

[lervag]

They will only work if you have UltiSnips and/or neosnippet installed.