Improve code generation documentation.

Author: brendandburns

README.md

@@ -156,10 +156,37 @@ Participation in the Kubernetes community is governed by the [CNCF Code of Condu
 
 # Development
 
-## Update the client
+## Update the generated code.
 
-To update the client clone the `gen` repo and run this command at the root of the client repo:
+The code is generated by the [swagger-codegen project](https://github.com/swagger-api/swagger-codegen).
 
-```bash
-${GEN_REPO_BASE}/openapi/java.sh kubernetes settings
+We have built general purpose cross-language tools for generating code, it is hosted in the
+[kubernetes-client/gen](https://github.com/kubernetes-client/gen) repository.
+
+To get started, in a root directory that is _not_ your `java` client directory, for example your
+directory layout could be:
+```
+${HOME}/
+        src/
+             gen/
+             java/
+...
+```
+
+Then to clone the `gen` repository, you would run:
+
+```sh
+cd ${HOME}/src
+git clone https://github.com/kubernetes-client/gen
+export GEN_ROOT=${PWD}
 ```
+
+Then to update the client:
+
+```sh
+cd ${HOME}/src/java
+${GEN_ROOT}/gen/openapi/java.sh kubernetes ./settings
+```
+
+This should run through a long-ish build process involving `docker` and eventually result in a new set of
+generated code in the `kubernetes` directory.