Dev Docs: REST: Add Security Note & Reindex Note

Added both notes to both JSON-RPC and REST docs.

Suggested by Jonas Schnelli (thanks!)

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

@@ -16,6 +16,9 @@ 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.
 
+The interface is not intended for public access and is only accessible
+from localhost by default.
+
 {{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

_includes/ref/bitcoin-core/rest/requests/get_tx.md

@@ -13,6 +13,8 @@ http://opensource.org/licenses/MIT.
 
 The `GET tx` operation {{summary_restTx}}
 
+{{reindexNote}}
+
 *Request*
 
 {% highlight text %}