graphics/nxwidgets/UnitTests: correct configuration option name in README.md
@@ -204,7 +204,7 @@ NXWidgets.:
requires large stacks. If you are using X11 in the simulation, make sure that
you set aside a "lot" of stack for the X11 system calls (maybe 8 or 16Kb).
The stack size for the thread that begins with user start is controlled by
- the configuration setting `CONFIG_USERMAIN_STACKSIZE`; you may need to
+ the configuration setting `CONFIG_INIT_STACKSIZE`; you may need to
increase this value to larger number to survive the X11 system calls.
If you are running X11 applications as NSH add-on programs, then the stack
