Update README for Go 1.6.

Author: ryszard

README.md

@@ -76,15 +76,16 @@ Longer term plans:
 
 ## Installation
 
-First, you need to set up your environment.
+First, you need to have Go installed. You can either follow the official [installation instructions](https://golang.org/doc/install) or, on OS X, just do
+```sh
+brew install go
+```
 
+As part of the initial setup, you have to set `GOPATH`, wihch is the location where Go keeps all its sources and binary artifacts.
 ```sh
 export GOPATH=...
-export GO15VENDOREXPERIMENT=1
 ```
 
-This is the location where Go keeps all its sources and binary artifacts: the doorman executable binary will go to `$GOPATH/bin/doorman`. `$GO15VENDOREXPERIMENT` needs to be set to allow easy vendoring (see https://golang.org/s/go15vendor). It will cease to be necessary as of Go 1.6.
-
 With this out of the way, Doorman is just one go get away:
 
 ```sh
@@ -98,6 +99,14 @@ mkdir -p $GOPATH/src/github.com/youtube
 git clone [email protected]:youtube/doorman.git
 ```
 
+### Go version <= 1.5
+
+If you are using a version of Go earlier than 1.6, you will need to set an environment variable to enable vendoring (see https://golang.org/s/go15vendor):
+
+```sh
+export GO15VENDOREXPERIMENT=1
+```
+
 ## Contributing
 
 See [CONTRIBUTING](CONTRIBUTING.md) for details on submitting patches and the contribution workflow.