Docs for v2.7.0 (#322)

* Docs for v2.7.0

* Document named-routes & invoke, polish reverse_proxy

* Storage import/export CLI docs

* Header replacement defer

* Proxy stream closing options, weighted round robin LB policy

src/docs/markdown/caddyfile/directives/acme_server.md

@@ -18,10 +18,14 @@ Using ACME server defaults, ACME clients should simply be configured to use `htt
 
 ```caddy-d
 acme_server [<matcher>] {
-	ca       <id>
-	lifetime <duration>
+	ca        <id>
+	lifetime  <duration>
+	resolvers <resolvers...>
 }
 ```
 
 - **ca** specifies the ID of the certificate authority with which to sign certificates. The default is `local`, which is Caddy's default CA, intended for locally-used, self-signed certificates, which is most common in dev environments. For broader use, it is recommended to specify a different CA to avoid confusion. If the CA with the given ID does not already exist, it will be created. See the [PKI app global options](/docs/caddyfile/options#pki-options) to configure alternate CAs.
+
 - **lifetime** (Default: `12h`) is a [duration](/docs/conventions#durations) which specifies the validity period for issued certificates. This value must be less than the lifetime of the [intermediate certificate](/docs/caddyfile/options#intermediate-lifetime) used for signing. It is not recommended to change this unless absolutely necessary.
+
+- **resolvers** are the addresses of DNS resolvers to use when looking up the TXT records for solving ACME DNS challenges. Accepts [network addresses](/docs/conventions#network-addresses) defaulting to UDP and port 53 unless specified. If the host is an IP address, it will be dialed directly to resolve the upstream server. If the hot is not an IP address, the addresses are resolved using the [name resolution convention](https://golang.org/pkg/net/#hdr-Name_Resolution) of the Go standard library. If multiple resolvers are specified, then one is chosen at random.