shrpx: Documented --spdy-bridge

src/shrpx.cc

@@ -527,6 +527,12 @@ void print_help(std::ostream& out)
       << "\n"
       << "  Mode:\n"
       << "    -s, --spdy-proxy   Enable secure SPDY proxy mode.\n"
+      << "    --spdy-bridge      Communicate with the backend in SPDY. Thus\n"
+      << "                       the incoming SPDY/HTTPS connections are\n"
+      << "                       converted to SPDY connection and relayed to\n"
+      << "                       the backend. See --backend-http-proxy-uri\n"
+      << "                       option if you are behind the proxy and want\n"
+      << "                       to connect to the outside SPDY proxy.\n"
       << "    --client           Instead of accepting SPDY/HTTPS connection,\n"
       << "                       accept HTTP connection and communicate with\n"
       << "                       backend server in SPDY. To use shrpx as\n"