Document dir listing optinos and _header.md and _footer.md

sites/werc.cat-v.org/docs/dir_listings.md

@@ -0,0 +1,29 @@
+Autogenerated Directory Listings
+================================
+
+If a directory has no `index.md`, `index.html` or `index.txt` and has no other
+*main handler* set up by a [werc app](/apps/), the default directory listing
+handler is used.
+
+The default directory handler simply displays the path to the directory, and a
+list of links to all files and dirs located at this path.
+
+
+Header and footer
+-----------------
+
+If a `_header.md` or `_footer.md` files are found in the directory, their
+contents will be displayed in the corresponding sections before and after
+the directory contents.
+
+
+Tuning the item's order
+------------------------
+
+You can set the `dir_listing_ls_opts` config variable in the dir's corresponding _werc/config to change the way items will be ordered.
+
+For example to list items in reverse chronological order simply add:
+
+    dir_listing_ls_opts=( -t )
+
+The options taken are [the standard Plan 9 ls(1) flags](http://man.cat-v.org/plan_9/1/ls).