add faq to address #490

docs/content/faq/multiple-protocol-listeners.md

@@ -0,0 +1,20 @@
+---
+title: "Handling Multiple Protocols"
+---
+
+It is quite possible for a single fabio instance to serve multiple protocols 
+via distinct listeners.
+
+In this example:
+```
+proxy.addr = 172.16.20.11:80;proto=http;rt=60s;wt=30s,\
+             172.16.20.11:443;proto=https;rt=60s;wt=30s;cs=all;tlsmin=10, \
+             172.16.20.11:8443;proto=tcp+sni
+```
+
+We are telling fabio to bind to `172.16.20.11` on three different ports 
+(`80`, `443`, and `8443`) using three distinct protocols 
+(`HTTP`, `HTTPS`, `TCP+SNI`).  You are free to bind to as many address, 
+port, and protocol combinations as needed within a single instance.
+
+See [#490](https://github.com/fabiolb/fabio/issues/490) for context.