Add more details to README

README.md

@@ -2,12 +2,31 @@
 
 Tokidoki is a (WIP) carddav and caldav server.
 
+## Architecture
+
+Tokidoki relies on [go-webdav][1] for the protocol implementation. It provides
+the storage backend and authentication, both of which are easily pluggable.
+
+It currently provides:
+
+Authentication:
+
+* IMAP (working)
+
+Storage:
+
+* Filesystem (working)
+* PostgreSQL (planned)
+
+[1]: https://github.com/emersion/go-webdav "go-webdav project page on Github"
+
 ## Building
 
 * `cd cmd/tokidoki && go build`
 
 ## Running
 
-Using the IMAP authentication backend and the filesystem storage backend:
+Using the IMAP authentication backend and the filesystem storage backend
+(directory must exist):
 
 * `./tokidoki -auth.url imaps://imap.example.com:993 -storage.url file:///path/to/storage -debug`