Update v3.5.5.md with summary

Author: andrew-platt

docs/changelogs/v3.5.5.md

@@ -42,7 +42,9 @@ See GitHub Actions
 
 ## Overview
 
-This release includes performance
+This release includes multiple small bug-fixes for compilation with CMake, compilation with the IFX compilers, file opening issues when OpenMP is used, and a couple of infrequent segmentation faults from improper usage.  One minor feature improvement is the increase in the number of output planes available in _FAST.Farm_ from 99 to 999.
+
+We recommend all users currently using any 3.5.x version to update to this version. There are no input files changes or API changes for calling from other codes since version 3.5.0.