update README, add usage instructions

README.md

@@ -2,4 +2,43 @@
 
 [![Build Status](https://travis-ci.org/lunduniversity/introprog-scalalib.svg?branch=master)](https://travis-ci.org/lunduniversity/introprog-scalalib)
 
-Library with Scala utilities for Computer Science teaching. The library is maintained by Björn Regnell at Lund University, Sweden. Contributions are welcome! For further information see: https://github.com/lunduniversity/introprog
+This is a library with Scala utilities for Computer Science teaching. The library is maintained by Björn Regnell at Lund University, Sweden. Contributions are welcome!
+
+The api documentation is available here: http://cs.lth.se/pgk/api/
+
+Se also: http://cs.lth.se/pgk and https://github.com/lunduniversity/introprog
+
+
+# Manual download
+
+Download the latest jar-file from here: https://github.com/lunduniversity/introprog-scalalib/releases
+
+Put the jar-file on your classpath when you run the Scala REPL, for example:
+```
+> scala -cp introprog_2.12-0.1.5.jar
+scala> val w = new introprog.PixelWindow()
+scala> w.fill(100,100,100,100,java.awt.Color.red)
+scala>
+```
+Put the jar-file on your classpath when you run your Scala app, for example:
+```
+> scala -cp "introprog_2.12-0.1.5.jar:." Main
+```
+If on Windows cmd/powershell use `;` instead of ´:´.
+
+# Using sbt
+
+If you have the [Scala Build Tool](https://www.scala-sbt.org/download.html) then you can put this text in a file called `build.sbt`
+```
+scalaVersion := "2.12.6"
+libraryDependencies += "se.lth.cs" %% "introprog" % "0.1.5"
+```
+
+When you run `sbt` in terminal the introprog lib is automatically downloaded and made available on your classpath.
+You can do things like:
+```
+> sbt
+sbt> console
+scala> val w = new introprog.PixelWindow()
+scala> w.fill(100,100,100,100,java.awt.Color.red)
+```