Update documentation to mention new command

README.md

@@ -8,9 +8,36 @@ my config scripts.
 
 ```bash
 ~$ git clone git@github.com:kirsle/.dotfiles
-~$ ./.dotfiles/setup --install
+~$ ./.dotfiles/setup
 ```
 
+# Dotfiles Manager (dfm)
+
+The dotfiles repo is managed by a `dfm` command, which gets installed into
+`~/bin` automatically. (The `.dotfiles/setup` script is just an easy alias
+to this command).
+
+See `dfm --help` for documentation. Briefly:
+
+* `dfm setup` creates symlinks to all the files in `./home` into `$HOME`.
+* `dfm update` does a `git pull` and installs any new dotfiles.
+* `dfm check-update` reminds you every 15 days to run `dfm update` (but
+  doesn't remind you more than once per 24 hours).
+
+In case one of the target files already exists (and is not a symlink), it is
+copied into `.dotfiles/backup` before being deleted and relinked.
+
+The commands take optional arguments:
+
+* `dfm setup --force`: forcefully re-link all dotfiles, deleting any links
+  that already exist.
+* `dfm setup --copy`: tell it not to use symlinks but instead make normal
+  file copies into `$HOME`.
+* `dfm check-update --force`: always show the update reminder.
+
+The `.dotfiles/setup` script passes all options along to `dfm`, so you can
+do `.dotfiles/setup --copy` for example.
+
 # Layout
 
 * `./setup`

home/bin/dfm

@@ -267,6 +267,9 @@ sub crawl {
         # Existing non-link targets should be backed up.
         if (-f $target && !-l $target) {
             print "Back up existing file to: $backup\n";
+            if (!-d $BACKUP) {
+                mkdir($BACKUP) unless $noop;
+            }
             copy($target, $backup) unless $noop;
             unlink($target) unless $noop;
         }