update README.vars

Change-Id: Ie2d0cc90ecc3e585a8fbfc9517e48170cf07c0d2

vcl/README.vars

@@ -5,6 +5,7 @@ General
 SAL_USE_VCLPLUGIN - use a VCL plugin
 SAL_NO_NWF - disable native widgets
 SAL_FORCEDPI - force a specific DPI (gtk & gtk3 plugins only)
+SAL_FORCE_HC - force high-contrast mode
 
 VCL_DOUBLEBUFFERING_AVOID_PAINT - don't paint the buffer, useful to see where we do direct painting
 VCL_DOUBLEBUFFERING_FORCE_ENABLE - enable double buffered painting
@@ -22,4 +23,4 @@ OpenGL
 SAL_FORCEGL - force enable OpenGL
 SAL_WITHOUT_WIDGET_CACHE - disable LRU caching of native widget texutres
 SAL_DISABLE_GLYPH_CACHING - don't render glyphs through OpenGL textures
-SAL_DISABLE_GL_WATCHDOG - don't start the thread that watches for broken GL drivers
\ No newline at end of file
+SAL_DISABLE_GL_WATCHDOG - don't start the thread that watches for broken GL drivers