Add version 1.21.10 details to the changelog

Author: JoelLefkowitz

docs/changelog.rst

@@ -2,6 +2,15 @@
 Changelog
 #########
 
+**********
+**1.21.10**
+**********
+
+**FIXED:** Fix type hints when using postponed evaluation of annotations (PEP-563) (:pr:`840`)
+**IMPROVED:** Update JSON & YAML renderers to not use a "." in their format string (:pr:`911`)
+**FIXED:** Fix lint errors when comparing types with == instead of is (:pr:`868`)
+**IMPROVED:** Update swagger-ui-dist to address CVE-2021-46708 (:pr:`904`)
+
 **********
 **1.21.9**
 **********