Update Readme about godeps in vendor

Author: bprashanth

README.md

@@ -9,7 +9,7 @@ that aren't part of the Kubernetes core.
 
 The code must be checked out as a subdirectory of `k8s.io`, and not `github.com`.
 
-```sh
+```shell
 mkdir -p $GOPATH/src/k8s.io
 cd $GOPATH/src/k8s.io
 # Replace "$YOUR_GITHUB_USERNAME" below with your github username
@@ -24,14 +24,38 @@ contrib contains multiple tiny projects, each with their own dependencies. Each
 in contrib/ has it's own Godeps.json. For example the Godeps.json for Ingress
 is Ingress/Godeps/Godeps.json. This means that godeps commands like `godep restore`
 or `godep test` work in the root directory. Theys should be run from inside the
-subproject directory you want to test
+subproject directory you want to test.
+
+## Prerequisites for updating Godeps
+
+Since we vendor godeps through `/vendor` vs the old style `Godeps/_workspace`, you either need a more recent install of go and godeps, or you need to set `GO15VENDOREXPERIMENT=1`. Eg:
+```shell
+$ godep version
+godep v74 (linux/amd64/go1.6.1)
+$ go version
+go version go1.6.1 linux/amd64
+$ godep save ./...
+```
+
+Will automatically save godeps to `vendor/` instead of `_workspace/`.
+If you have an older version of go, you must run:
+```shell
+$ GO15VENDOREXPERIMENT=1 godep save ./...
+```
+
+If you have an older version of godep, you must update it:
+```shell
+$ go get github.com/tools/godep
+$ cd $GOPATH/src/github.com/tools/godep
+$ go build -o godep *.go
+```
 
 ## Updating Godeps
 
 The most common dep to update is obviously going to be kuberetes proper. Updating
 kubernetes and it's dependancies in the Ingress subproject for example can be done
-as follows:
-```
+as follows (the example assumes you Kubernetes repo is rooted at `$GOPATH/src/github.com/kubernetes`, `s/github.com\/kubernetes/k8s.io/` as required):
+```shell
 cd $GOPATH/src/github.com/kubernetes/contrib/ingress
 godep restore
 go get -u github.com/kubernetes/kubernetes
@@ -46,7 +70,7 @@ git commit
 
 Other deps are similar, although if the dep you wish to update is included from
 kubernetes we probably want to stay in sync using the above method. If the dep is not in kubernetes proper something like the following should get you a nice clean result:
-```
+```shell
 cd $GOPATH/src/github/kubernetes/contrib/ingress
 godep restore
 go get -u $SOME_DEP
@@ -59,6 +83,6 @@ git commit
 ## Running all tests
 
 To run all go test in all projects do this:
-```
+```shell
 ./hack/for-go-proj.sh test
 ```