Add warning about using existing tag names for taxonomies

[steveparks]

At the moment there is no disambiguation between tags for taxonomies and tags for system tags within views.

So a taxonomy called 'Section' can't be referenced as {{ section }} <li> ... </li> {{ /section }} in views because it conflicts with the existing Statamic system tag {{ section }}.

There is a way to disambiguate between variables and tags, but not between types of tags.

I've submitted an idea to provide this disambiguation: statamic/ideas#1195

But in the meantime, I suggest adding this warning to the taxonomy page to avoid people getting in a pickle.

[sjclark]

To be fair Statamic does advise not to use the names of tags as field names, but maybe that should be expanded to be a bit broader (beyond just field names). Generally using the same names in various places is probably going to break something eventually 😂 https://statamic.dev/tips/reserved-words