Add info on plugins (including interceptors) #17
Description
Interceptor content was removed in 19a9589 (see comment below for why).
Should add back in proper plugin level explanation.
It's rare to create activity and workflow interceptors independently, would suggest not encouraging it. This is also missing client interceptors and Nexus interceptors. This is also missing discussion of plugins which is a good way to configure interceptors.
Originally posted by @cretz in #4 (comment)