Document how to generate dependencies (#13)

* Document how to generate dependencies

Signed-off-by: Pavol Loffay <ploffay@redhat.com>

* Change find command

Signed-off-by: Pavol Loffay <ploffay@redhat.com>

Author: pavolloffay

README.md

@@ -57,10 +57,25 @@ $ docker run --rm jaegertracing/protobuf --help
 
 Example for Java:
 ```
-docker run --rm -v${PWD}:{PWD} -w${PWD} jaegertracing/protobuf:latest --proto_path=${PWD} \
+docker run --rm -u $(id -u) -v${PWD}:${PWD} -w${PWD} jaegertracing/protobuf:latest --proto_path=${PWD} \
     --java_out=${PWD} -I/usr/include/github.com/gogo/protobuf ${PWD}/model.proto
 ```
 
 CLI options:
 - `--proto_path`: The path where protoc should search for proto files
 - `--java_out`  : Generate Java code in the provided path
+
+#### Generate dependencies
+
+The generated code might require dependencies on packages like GoGo or Swagger.
+The code for these modules can be also generated by using this docker image:
+
+```
+docker run --rm -u $(id -u) -v${PWD}:${PWD} -w${PWD} jaegertracing/protobuf:latest --proto_path=${PWD} \
+    --java_out=${PWD} /usr/include/github.com/gogo/protobuf/gogoproto/gogo.proto
+```
+
+Use this command to find the path to proto files included in the image:
+```
+docker run --rm -it --entrypoint=/bin/sh jaegertracing/protobuf:latest -c "find /usr/include -name *.proto"
+```