diff --git a/hgwebdir.cgi b/hgwebdir.cgi
--- a/hgwebdir.cgi
+++ b/hgwebdir.cgi
@@ -8,10 +8,21 @@ cgitb.enable()
 # sys.path.insert(0, "/path/to/python/lib") # if not a system-wide install
 from mercurial import hgweb
 
-# The config file looks like this:
+# The config file looks like this.  You can have paths to individual
+# repos, collections of repos in a directory tree, or both.
+#
 # [paths]
 # virtual/path = /real/path
 # virtual/path = /real/path
+#
+# [collections]
+# /prefix/to/strip/off = /root/of/tree/full/of/repos
+#
+# collections example: say directory tree /foo contains repos /foo/bar,
+# /foo/quux/baz.  Give this config section:
+#   [collections]
+#   /foo = /foo
+# Then repos will list as bar and quux/baz.
 
 # Alternatively you can pass a list of ('virtual/path', '/real/path') tuples
 # or use a dictionary with entries like 'virtual/path': '/real/path'