Add in-repo BIP70 extension registration page

bip-0070.mediawiki

@@ -252,10 +252,10 @@ message with version=2. Old implementations should let the user know
 that they need to upgrade their software when they get an up-version
 PaymentDetails message.
 
-Implementations that need to extend messages in this specification
+Implementations that need to extend messages in this specification shall use
-shall use tags starting at 1000, and shall update the wiki page at
+tags starting at 1000, and shall update the
-https://en.bitcoin.it/wiki/Payment_Request to avoid conflicts with
+[[bip-0070/extensions.mediawiki|extensions page]] via pull-req to avoid
-other extensions.
+conflicts with other extensions.
 
 ==References==
 

bip-0070/extensions.mediawiki

@@ -0,0 +1,9 @@
+==BIP70 Extensions==
+
+Add your extension below using tags starting at 1000 and submit a pull-req.
+
+{|
+| Field Number || Extension Name || Field Name || Description
+|-
+| 1000 || [[https://example.com|(unassigned)]] || (unassigned) || (unassigned)
+|}

bip-0070/paymentrequest.proto

@@ -1,9 +1,9 @@
 //
 // Simple Bitcoin Payment Protocol messages
 //
-// Use fields 100+ for extensions;
+// Use fields 1000+ for extensions;
-// to avoid conflicts, register extensions via pull-req at:
+// to avoid conflicts, register extensions via pull-req at
-// https://github.com/bitcoin/bips
+// https://github.com/bitcoin/bips/bip-0070/extensions.mediawiki
 //
 
 package payments;