Clarify documentation of the auto_reload option

Created by: fvsch

Thanks a lot for this lib! I'm using it to render component templates that will also be rendered by TwigPHP, and it's working well so far.

I've had the exact same issue as #194 (closed) (with the same use case: an express middleware to use with a webpack dev server) and spent a good hour trying every option and possible fix I could think of. My fix was indeed to recreate the Twing environement on every request.

The current documentation says:

auto_reload boolean When developing with Twing, it’s useful to recompile the template whenever the source code changes. If you don’t provide a value for the auto_reload option, it will be determined automatically based on the debug value.

Reading through #194 (closed) and https://github.com/twigphp/Twig/issues/2697 it seems auto_reload only affects the cache behavior, and can be used to bypass the cache if a template file was changed, but there is another in-memory cache attached to the environment that it does not affect at all? How could that be reflected more clearly in the docs, maybe with a warning for long-lived Twing environments?