Update documentation with instructions for Angie (nginx)

Hi guys. I know it was discussed in #4919 #5467 I start use an Angie as if I understood correctly nginx developers have some organization issues. Core members from nginx team moved to Angie project that is a "direct replacement" kind of.

Did you rethink your position of nginx direct replacements support? If it stays the same I would appreciate if you give me any advice how can I use certbot with Angie. Thank you