add installation instructions

fixes #6

README.md

@@ -5,8 +5,21 @@ chat software.
 
 ![Screenshot](https://i.imgur.com/B8ldT5k.png)
 
+## Installation
+
+Requirements:
+
+1. [Go](https://golang.org/)
+2. [Git](https://git-scm.com/)
+3. [Opus](https://opus-codec.org/) development headers
+4. [OpenAL](http://kcat.strangesoft.net/openal.html) development headers
+
+To fetch and build:
+
     go get -u layeh.com/barnard
 
+After running the command above, `barnard` will be compiled as `$(go env GOPATH)/bin/barnard`.
+
 ## License
 
 GPLv2