Better documentation for persisting --type-add/--type-clear using config files.

[llamasoft]

A while back I discovered that ripgrep supports a --type-add option and I was quite excited. I find myself using the same glob patterns pretty regularly, so having a way to define common patterns seemed like it would save me a tremendous amount of time... until I saw that "Type settings are NOT persisted".
I found this rather disappointing because it meant that --type-add would only ever save time if I wrapped rg in an alias or function.
It wasn't until much later (today in fact!) that I saw that ripgrep supports configuration files. This effectively means that I can persist my type definitions.

Given the severe limitation of type definitions not being automatically persisted, I would strongly suggest updating the help text/manpages of --type-add and --type-clear to also mention the existence of using a configuration file as a workaround. Yes, the configuration file guide uses --type-add as an example, but most users may not realize that a configuration file solution exists if something doesn't point them directly to it.

In summary, I suggest changing this line:

Note that this MUST be passed to every invocation of ripgrep. Type settings are NOT persisted.

Into something like this:

Note that this MUST be passed to every invocation of ripgrep. Type settings are NOT persisted. See CONFIGURATION FILES for a workaround.

[BurntSushi]

Sounds good. For such a small change, I'd encourage folks to submit a PR for it.