Update document.

Author: moriyoshi

README.md

@@ -8,14 +8,16 @@ It has the following features:
 
 * URL rewriting
 
-  If the upstream HTTP server listens on `127.0.0.1:3000` and you want to get your browser to access to it by a request to `http://example.com`, the configuration should look as follows:
+  If you want to get your browser to access to the upstream HTTP server listening on `127.0.0.1:3000` by a request to `http://example.com`, the configuration should look as follows:
 
   ```
   hosts:
     http://example.com:
       - ^(/*)$: http://127.0.0.1:3000$1
   ```
 
+  This can be done since the name resolution is done in devproxy, which is configured to map any request for http://example.com to http://127.0.0.1:3000.
+
 * Transparent TLS wrapping (simulation of an SSL/TLS-enabled environment)
 
   You can also make it possible to direct the request to `https://example.com/` to the upstream by adding the configuration like the following:
@@ -28,7 +30,7 @@ It has the following features:
       - ^(/*)$: http://127.0.0.1:3000$1
   ```
 
-  It is however necessary to set up the private PKI for issuing bogus server certificates and let your browser trust the PKI's root CA certificate.  **DO IT ON YOUR OWN RISK.**
+  Even though you don't have a valid certificate prepared for `example.com`, devproxy automatically generates it on the fly.  However, it is necessary to set up the private PKI for issuing bogus server certificates and let your browser trust the PKI's root CA certificate.  **DO IT ON YOUR OWN RISK.**
 
   The CA for issuing bogus server certificates is configured as follows:
 
@@ -68,6 +70,45 @@ It has the following features:
           X-Cgi-Path-Info: $3
 ```
 
+* Proxy chaining
+
+  You can direct outgoing requests to another proxy server.  This is useful in a restricted network environment.
+
+  ```
+proxy:
+  http: http://anoother-proxy-server:8080
+  https: http://another-proxy-server:8080
+```
+
+  `excluded` directive can be used when you want to prevent the requests to the specific hosts from being proxied.
+   
+  ```
+  excluded: 
+    - 127.0.0.1
+    - localhost
+    - intranet.example.com 
+```
+
+  Or inversely, in case of whitelisting:
+
+  ```
+  included: 
+    - intranet.example.com
+    - foobar.example.com
+```
+
+  TLS proxy can also be specified.
+
+  ```
+  proxy:
+    http: https://anoother-proxy-server:8443
+    https: https://another-proxy-server:8443
+    tls:
+      ca_certs: cabundle.crt.pem
+      certs:
+       - cert: client_crt.pem # this can be either the filename of a PEM-formatted certificate or a PEM string itself.
+         key: client_key.pem # this can be either the filename of a PEM-formatted private key or a PEM string itself.
+```
 
 ## Installation