Add changelog

Author: bartelink

RELEASE_NOTES.md

@@ -1,6 +1,9 @@
+### 6.1.3
+* Add ParseResults.GetResult(expr, defaultThunk) [#187](https://github.com/fsprojects/Argu/pull/187)
+
 ### 6.1.2
-* Fix Mandatory arguments in nested subcommands. [#116](https://github.com/fsprojects/Argu/issues/116)
-* Fix Consistent handling of numeric decimal separators using invariant culture. [#159](https://github.com/fsprojects/Argu/issues/159)
+* Fix Mandatory arguments in nested subcommands. [#116](https://github.com/fsprojects/Argu/issues/116) [@chestercodes](https://github.com/chestercodes) 
+* Fix Consistent handling of numeric decimal separators using invariant culture. [#159](https://github.com/fsprojects/Argu/issues/159) [@stmax82](https://github.com/stmax82)
 
 ### 6.1.1
 * Fix CustomAssignmentOrSpacedAttribute interop with optional fields.