Add documentation

scripts/remove_session

@@ -1,5 +1,29 @@
 #!/usr/bin/perl
 
+=head1 SYNOPSIS
+
+remove_session [--age time] [session_ids ...]
+
+=head1 DESCRIPTION
+
+The C<remove_session> script removes the specified sessions from the
+simba database and then cleans up orphaned entries.
+
+The sessions can be specified by minimum age or by listing their ids (or
+both, but that is probably not very useful).
+
+The age is specified as a fractional number followed by a unit: "y",
+"m", "w", or "d". So C<remove_session --age 2.5y> removes all sessions
+older than 2.5 years (actually 2.5 * 365 * 86400 seconds -- leap years
+and DST are ignored), and C<remove_session --age 52w> removes all
+sessions older than 52 weeks.
+
+If neither the age nor a list of sessions is specified, no sessions are
+removed, but the cleanup phase is still run, which may take considerable
+time (and might be considered a bug).
+
+=cut
+
 # This script removes all data associated with the given sessions.
 # For each session it first removes all instances of that session and
 # then cleans up any orphans.
@@ -10,6 +34,7 @@ use strict;
 use Simba::CA;
 use Bit::Vector::Judy;
 use Getopt::Long;
+use Pod::Usage;
 
 
 $| = 1;
@@ -24,7 +49,13 @@ my $partition_size = $ca->{instances_part_size};
 my %opt;
 GetOptions(
     \%opt,
-    "age=s");
+    "age=s",
+    "help",
+) or pod2usage(verbose => 0);
+
+if ($opt{help}) {
+    pod2usage(verbose => 2);
+}
 
 if ($opt{age}) {
     my ($num, $unit) = $opt{age} =~ /(\d(?:.\d+)?)(y|m|w|d)/;