update README

README.md

 # wireguard-formula
 
-currently with only `_modules` and `_states`.
+Installs WireGuard (usually dkms and utils), and creates interfaces plus peers.
 
-# Install
+See the full [Salt Formulas installation and usage instructions](http://docs.saltstack.com/en/latest/topics/development/conventions/formulas.html).
 
-Add the path to the wireguard-formula to the master configuration file under option
-`file_roots` or as `gitfs_remotes`.
+# Configuration
 
-# Use as module
+All configuration is done via pillar data. See `pillar.example` for examples.
+
+# Available states
+
+## `wg.present (name, listen_port, fwmark, private_key, preshared_key)`
+
+Creates a wireguard interface and sets interface-wide parameters.
+
+## `wg.peer_present (name, interface, endpoint, persistent_keepalive, allowed_ips)`
+
+Adds a peer to an interface and sets peer-specific parameters.
+
+## `wg.absent (name)`
+
+Removes a wireguard interface.
+
+## `wg.peer_absent (name, interface)`
+
+Removes a peer from an interface.
+
+# Excerpt of a few available module functions
 
 `salt-call wg.create wgtest`
+
 `salt-call wg.show wgtest`
-`salt-call wg.set interface listen_port=1337`
-`salt-call wg.delete wgtest`
 
-# Use as state
+`salt-call wg.set interface listen_port=1337`
 
-```
-wgtest:
-  wg.present:
-    - listen_port: 1337
+`salt-call wg.delete wgtest`
 
-1ymBfBty05PNhD/QJKUlu4aL2p4jKSWVVqVQWIQG6wM=:
-  wg.peer_present:
-    - interface: wgtest
-```