add gitcommit highlights

runtime/queries/gitcommit/highlights.scm

@@ -0,0 +1,18 @@
+(subject) @markup.heading
+(path) @string.special.path
+(branch) @string.special.symbol
+(commit) @constant
+(item) @markup.link.url
+(header) @tag
+
+(change kind: "new file" @diff.plus)
+(change kind: "deleted" @diff.minus)
+(change kind: "modified" @diff.delta)
+(change kind: "renamed" @diff.delta.moved)
+
+[":" "->"] @punctuation.delimeter
+(comment) @comment
+
+; once we have diff injections, @comment should become @none
+((comment (scissors))
+ (message)+ @comment)