add installation options to the readme

README.md

@@ -3,6 +3,14 @@
 A [timetrap](https://github.com/samg/timetrap/) compatible command line time
 tracking application.
 
+## Installation
+
+If you're a [rust](https://rust-lang.org) programmer you can do
+
+    cargo install tiempo
+
+Ir if you use archlinux, there's a `tiempo-git` package in the AUR.
+
 ## Tutorial
 
 First of all, you can abbreviate all commands to their first letter, so `t in`