update changelog

Author: tjex

CHANGELOG.md

@@ -13,6 +13,7 @@ Format: `<description> (by <contributor>, <pr number>)`
 
 - Ignore commented links for LSP diagnostics. Use an AST to parse files, fixing
   other similar edge cases. (by @WhyNotHugo, 638)
+- Links in markdown footnotes now included in :ZkLinks (by @WhyNotHugo, 639)
 
 
 ## 0.15.2