edit megachange description (add 'P2P exchange')

_data/merchants.yml

@@ -43,7 +43,7 @@
       url: https://localmonero.co/
     - name: Magnetic Exchange
       url: https://magneticexchange.com
-    - name: MegaChange.is
+    - name: MegaChange.is (P2P exchange)
       url: https://megachange.is
     - name: MoneroDirect (Euro only)
       url: https://monerodirect.com