Adjust the sip-template

Author: bracevac

sip-template.md

@@ -1,10 +1,11 @@
 ---
 layout: sip
+number: NN
 permalink: /sips/:title.html
 stage: implementation
 status: waiting-for-implementation
 presip-thread: https://contributors.scala-lang.org/t/pre-sip-foo-bar/9999
-title: SIP-NN - Title of the Proposal
+title: Title of the Proposal
 ---
 
 **By: Author A and Author B and Author C**