Extend the readme.

README.md

@@ -1,3 +1,41 @@
 # autobookmarks
 
 Like `recentf` but better.
+
+# How it works
+
+This package doesn't provide any UI, it only implements the back-end
+"store" and an API you can use to retrieve the bookmarks.
+
+The two main functions are `abm-visited-buffers` and
+`abm-recent-buffers` to retrieve lists of visited and recent buffers.
+
+This package automatically adds all killed buffers, according to
+`abm-killed-buffer-functions`, to the list of recent buffers.  When
+you visit a recent buffer, its associated bookmark is removed from the
+recent list and moved to the visited list.  When you kill a visited
+buffer, its associated bookmark is moved to the recent list.
+
+When you visit a new buffer which is not recent it is added, according
+to `abm-visited-buffer-hooks`, to the visited list.  This ensures that
+newly opened buffers are stored in case of a crash.  When you restart
+emacs, they will be available as recent buffers (they are not stored
+as recent right away because they are active and so shouldn't be on
+the recent list---that list only stores buffers which aren't visited)
+
+You can restore a recent (killed) buffer by using
+`abm-restore-killed-buffer` to which you pass the stored bookmark.
+
+You can toggle this mode on and off by using `autobookmarks-mode`,
+which is a global minor mode.
+
+# The (lack of) UI
+
+The author uses `sallet` package to provide seamless integration of
+bookmarks with buffer switching/finding files.  You can write an `ido`
+or `helm` interface fairly easily.  If someone does so, feel free to
+contribute it back as a patch.
+
+The data is stored in the same format as emacs bookmarks (`(info
+"(emacs) Bookmarks")`), so it should be possible to add a bookmark
+interface for it as well.