documented reason for preload of libdrm.so.2

Dockerfile

@@ -29,6 +29,7 @@ RUN apt-get update && apt-get install --yes --no-install-recommends \
 USER player
 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
 # X Error: BadAccess (attempt to access private resource denied) 10
 # X Error: BadShmSeg (invalid shared segment parameter) 128