mw/*: updates docs about upstream (#968)

Upstream allows file structured like /etc/resolv.conf. Update docs.

Fixes #709

middleware/auto/README.md

@@ -31,7 +31,8 @@ are used.
 * `no_reload` by default CoreDNS will reload a zone from disk whenever it detects a change to the
   file. This option disables that behavior.
 * `upstream` defines upstream resolvers to be used resolve external names found (think CNAMEs)
-  pointing to external names.
+  pointing to external names. **ADDRESS** can be an IP address, and IP:port or a string pointing to
+  a file that is structured as /etc/resolv.conf.
 
 All directives from the *file* middleware are supported. Note that *auto* will load all zones found,
 even though the directive might only receive queries for a specific zone. I.e:

middleware/file/README.md

@@ -39,7 +39,8 @@ file DBFILE [ZONES... ] {
   file. This option disables that behavior.
 * `upstream` defines upstream resolvers to be used resolve external names found (think CNAMEs)
   pointing to external names. This is only really useful when CoreDNS is configured as a proxy, for
-  normal authoritative serving you don't need *or* want to use this.
+  normal authoritative serving you don't need *or* want to use this. **ADDRESS** can be an IP
+  address, and IP:port or a string pointing to a file that is structured as /etc/resolv.conf.
 
 ## Examples
 

middleware/kubernetes/README.md

@@ -24,10 +24,10 @@ kubernetes [ZONES...] {
     resyncperiod DURATION
     endpoint URL
     tls CERT KEY CACERT
-    namespaces NAMESPACE [NAMESPACE...]
+    namespaces NAMESPACE...
     labels EXPRESSION
     pods POD-MODE
-    upstream ADDRESS [ADDRESS...]
+    upstream ADDRESS...
     fallthrough
 }
 ```

middleware/secondary/README.md

@@ -26,7 +26,8 @@ secondary [zones...] {
 * `transfer to` can be enabled to allow this secondary zone to be transferred again.
 * `upstream` defines upstream resolvers to be used resolve external names found (think CNAMEs)
   pointing to external names. This is only really useful when CoreDNS is configured as a proxy, for
-  normal authoritative serving you don't need *or* want to use this.
+  normal authoritative serving you don't need *or* want to use this. **ADDRESS** can be an IP
+  address, and IP:port or a string pointing to a file that is structured as /etc/resolv.conf.
 
 ## Examples