Add "other" header above unsorted links

This makes it valid markdown and prevents the behavior of some renderers
where each bullet gets rendered as a separate paragraph.

Author: tmandry

templates/relnotes.md

@@ -6,20 +6,23 @@ Language
 **relnotes**
 {{language_relnotes}}
 
+**other**
 {{language_unsorted}}
 
 Compiler
 --------
 **relnotes**
 {{compiler_relnotes}}
 
+**other**
 {{compiler_unsorted}}
 
 Libraries
 ---------
 **relnotes**
 {{libraries_relnotes}}
 
+**other**
 {{libraries_unsorted}}
 
 Stabilized APIs
@@ -30,6 +33,7 @@ Cargo
 **relnotes**
 {{cargo_relnotes}}
 
+**other**
 {{cargo_unsorted}}
 
 Misc
@@ -40,13 +44,15 @@ Compatibility Notes
 **relnotes**
 {{compat_relnotes}}
 
+**other**
 {{compat_unsorted}}
 
 UNSORTED
 --------
 **relnotes**
 {{unsorted_relnotes}}
 
+**other**
 {{unsorted}}
 
 {{links}}