Dev Docs: Add REST Documentation

* Uses same basic format as JSON-RPC documentation.

Closes #715

_includes/ref/bitcoin-core/rest/intro.md

@@ -0,0 +1,29 @@
+{% comment %}
+This file is licensed under the MIT License (MIT) available on
+http://opensource.org/licenses/MIT.
+{% endcomment %}
+{% assign filename="_includes/ref/bitcoin-core/rest/intro.md" %}
+
+### HTTP REST
+{% include helpers/subhead-links.md %}
+
+{% autocrossref %}
+
+As of [version 0.10.0][bitcoin core 0.10.0], Bitcoin Core provides
+an **unauthenticated** HTTP REST interface.  The interface runs on the
+same port as the JSON-RPC interface, by default port 8332 for mainnet and
+port 18332 for testnet. It must be enabled by either starting Bitcoin
+Core with the `-rest` option or by specifying `rest=1` in the
+configuration file.
+
+{{WARNING}} A web browser can access a HTTP REST interface running on
+localhost, possibly allowing third parties to use cross-site scripting
+attacks to download your transaction and block data, reducing your
+privacy.  If you have privacy concerns, you should not run a browser on
+the same computer as a REST-enabled Bicoin Core node.
+
+The interface uses standard [HTTP status
+codes](https://en.wikipedia.org/wiki/List_of_HTTP_status_codes) and
+returns a plain-text description of errors for debugging.
+
+{% endautocrossref %}