documented reason for QT_X11_NO_MITSHM=1

Dockerfile

@@ -31,6 +31,8 @@ VOLUME /toontown-rewritten/engine
 WORKDIR /toontown-rewritten/engine
 # symbol lookup error: /usr/lib/x86_64-linux-gnu/libGLX_mesa.so.0: undefined symbol: drmGetDevice2
 ENV LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libdrm.so.2
+# disable shared memory between xorg client & server
+# https://en.wikipedia.org/wiki/MIT-SHM
 # X Error: BadAccess (attempt to access private resource denied) 10
 # X Error: BadShmSeg (invalid shared segment parameter) 128
 # X Error: BadDrawable (invalid Pixmap or Window parameter) 9