doc: write goals in readme

README.md

@@ -1,2 +1,31 @@
-# rieter
+# Rieter
 
+Rieter is both a Pacman repository server, as well as a build system for Pacman
+packages.
+
+## Goals
+
+### Repository server
+
+My first goal for this project is to create a convenient all-round repository
+server implementation that could be used for everything from self-hosting a
+local repository to managing an entire distribution's package repository. It
+should be easy to deploy, lightweight, and work with any distribution. It
+should support any number of repositories and packages, and work with any
+package architecture.
+
+The repositories can be populated by manually uploading packages to the server
+(e.g. from a CI build), or by mirroring already existing repositories. The
+mirroring feature in particular makes it trivial to set up a new mirror for a
+distribution, as the server would take care of keeping the mirror up-to-date.
+Another usecase for this would be creating a local mirror of your
+distribution's repositories, which can greatly reduce your update times
+depending on your internet connection.
+
+### Build system
+
+The second goal is to create an easy-to-use build system for Pacman packages.
+This could for example be used to automatically build AUR packages and publish
+them to one of your repositories. This can greatly reduce update times, as you
+no longer need to build AUR packages locally, as this automatically happens "in
+the cloud".