Configure: added gRPC module help message.

auto/options

diff --git a/auto/options b/auto/options
index 2535741..59f0449 100644
--- a/auto/options
+++ b/auto/options
@@ -473,6 +473,7 @@
   --without-http_fastcgi_module      disable ngx_http_fastcgi_module
   --without-http_uwsgi_module        disable ngx_http_uwsgi_module
   --without-http_scgi_module         disable ngx_http_scgi_module
+  --without-http_grpc_module         disable ngx_http_grpc_module
   --without-http_memcached_module    disable ngx_http_memcached_module
   --without-http_limit_conn_module   disable ngx_http_limit_conn_module
   --without-http_limit_req_module    disable ngx_http_limit_req_module