Backends, Examples: Add comments about using WndProc handler and WantCaptureXXX flags. (#5061)

+ update README.

examples/example_glut_opengl2/main.cpp

@@ -94,8 +94,8 @@ void glut_display_func()
 }
 
 // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
-// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
-// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
+// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application, or clear/overwrite your copy of the mouse data.
+// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
 // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
 
 int main(int argc, char** argv)
@@ -125,6 +125,7 @@ int main(int argc, char** argv)
     //ImGui::StyleColorsClassic();
 
     // Setup Platform/Renderer backends
+    // FIXME: Consider reworking this example to install our own GLUT funcs + forward calls ImGui_ImplGLUT_XXX ones, instead of using ImGui_ImplGLUT_InstallFuncs().
     ImGui_ImplGLUT_Init();
     ImGui_ImplGLUT_InstallFuncs();
     ImGui_ImplOpenGL2_Init();