docs: clarify origin and purpose of this fork

Author: buchdag

README.md

@@ -2,6 +2,10 @@
 
 [Foreman](https://github.com/ddollar/foreman) in Go.
 
+This project was forked from [ddollar/forego](https://github.com/ddollar/forego).
+
+It does not accept issues because its sole purpose is to have a working and maintained version of forego for [nginx-proxy/nginx-proxy](https://github.com/nginx-proxy/nginx-proxy).
+
 ##### Compile from Source
 
     $ go get -u github.com/nginx-proxy/forego