[Driver] Add help text for -no-color-diagnostics flag

Author: broadwaylamb

include/swift/Option/Options.td

@@ -304,7 +304,8 @@ def color_diagnostics : Flag<["-"], "color-diagnostics">,
   Flags<[FrontendOption, DoesNotAffectIncrementalBuild]>,
   HelpText<"Print diagnostics in color">;
 def no_color_diagnostics : Flag<["-"], "no-color-diagnostics">,
-  Flags<[FrontendOption, DoesNotAffectIncrementalBuild]>;
+  Flags<[FrontendOption, DoesNotAffectIncrementalBuild]>,
+  HelpText<"Do not print diagnostics in color">;
 
 def module_cache_path : Separate<["-"], "module-cache-path">,
   Flags<[FrontendOption, DoesNotAffectIncrementalBuild, ArgumentIsPath]>,