Make note of Apache configuration for Authorization in the docs

[weierophinney]

I was struggling for multiple hours with the Basic Authorization which was perfectly working locally, but not in production. Found a that the solution was very simple, but hard to find:

http://briangallagher.ie/2015/01/26/apigility-constant-403-forbidden/

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Originally posted by @storeman at zfcampus/zf-apigility#180