Update release notes

RELEASE_NOTES.md

@@ -8,6 +8,7 @@ Version 1.1 (under testing, stable)
 * Bug fix: Path of search.html in search form action should always be absolute
 * Bug fix: Copyright meta tag should be set to the author, instead of the license
 * Bug fix: Close meta tags
+* Bug fix: ID of search form in 404 page should be different from the ID of search form in main navigation
 
 Version 1.0
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