Add new docker link, DO link, and enhanced comment

README.md

@@ -52,7 +52,7 @@ Caddy is available as a Docker container from any of these sources:
 - [abiosoft/caddy](https://registry.hub.docker.com/u/abiosoft/caddy/)
 - [darron/caddy](https://registry.hub.docker.com/u/darron/caddy/)
 - [jumanjiman/caddy](https://registry.hub.docker.com/u/jumanjiman/caddy/)
-
+- [zenithar/nano-caddy](https://registry.hub.docker.com/u/zenithar/nano-caddy/)
 
 
 #### 3rd-party libraries
@@ -118,6 +118,8 @@ This project would not be what it is without your help. Please see the [contribu
 
 Thanks for making Caddy -- and the Web -- better!
 
+Special thanks to [![DigitalOcean](http://i.imgur.com/sfGr0eY.png)](https://www.digitalocean.com) for hosting the Caddy project.
+
 
 
 

middleware/replacer.go

@@ -24,7 +24,9 @@ type replacer struct {
 // NewReplacer makes a new replacer based on r and rr.
 // Do not create a new replacer until r and rr have all
 // the needed values, because this function copies those
-// values into the replacer.
+// values into the replacer. rr may be nil if it is not
+// available. emptyValue should be the string that is used
+// in place of empty string (can still be empty string).
 func NewReplacer(r *http.Request, rr *responseRecorder, emptyValue string) Replacer {
 	rep := replacer{
 		replacements: map[string]string{