releasenotes.txt: add notes (GUI, polyspace suppressions) [skip ci]

Author: danmar

releasenotes.txt

@@ -1,27 +1,17 @@
 
 Release Notes for Cppcheck 2.20
 
-Major bug fixes & crashes:
--
-
-New checks:
--
-
-C/C++ support:
--
-
 GUI:
--
+- Fix: The Misra C checkbox in "Edit Project" dialog is unchecked after reloading project.
+- Fix: In the Misra Report, use proper icons according to misra classifications
+- Fix: The platform files are not shown in the dropdown in ProjectFileDialog
+- Troubleshooting: detailed progress view that shows what files the threads are working on
 
 Changed interface:
 - removed CMake option "DISABLE_CRTDBG_MAP_ALLOC"
 - CMake option "BUILD_TESTS" has been deprecated and will be removed in Cppcheck 2.22 - use "BUILD_TESTING" instead
--
-
-Infrastructure & dependencies:
--
 
 Other:
 - The built-in "win*" and "unix*" platforms will now default to signed char type instead of unknown signedness. If you require unsigned chars please specify "--funsigned-char"
 - bumped minimum required CMake version to 3.22
--
+- Support inline polyspace suppressions