Update description of how ack works without a file

Changes

@@ -11,12 +11,15 @@ a --context=5 in your ackrc.  Thanks, Ed Avis.  (GH #595)
 t/ack-s.t would fail in non-English locales.  Thanks, Olivier Mengué.
 (GH #485, GH #515)
 
-
 [ENHANCEMENTS]
 --after-context and --before-context (and their short counterparts
 -A and -B) no longer require a value to be passed.  If no value is
 set, they default to 2. (GH #351)
 
+[DOCUMENTATION]
+Updated incorrect docs about how ack works.  Thanks, Gerhard Poul.
+(GH #543)
+
 
 2.16    Fri Mar 10 13:32:39 CST 2017
 ====================================

ack

@@ -1068,9 +1068,9 @@ ack - grep-like text finder
 
 Ack is designed as an alternative to F<grep> for programmers.
 
-Ack searches the named input FILEs (or standard input if no files
-are named, or the file name - is given) for lines containing a match
-to the given PATTERN.  By default, ack prints the matching lines.
+Ack searches the named input FILEs or DIRECTORYs for lines containing a
+match to the given PATTERN.  By default, ack prints the matching lines.
+If no FILE or DIRECTORY is given, the current directory will be searched.
 
 PATTERN is a Perl regular expression.  Perl regular expressions
 are commonly found in other programming languages, but for the particulars
@@ -2227,6 +2227,10 @@ L<http://cpanratings.perl.org/d/ack>
 
 L<http://search.cpan.org/dist/ack>
 
+=item * MetaCPAN
+
+L<http://metacpan.org/release/ack>
+
 =item * Git source repository
 
 L<https://github.com/petdance/ack2>
@@ -2238,6 +2242,7 @@ L<https://github.com/petdance/ack2>
 How appropriate to have I<ack>nowledgements!
 
 Thanks to everyone who has contributed to ack in any way, including
+Gerhard Poul,
 Ethan Mallove,
 Marek Kubica,
 Ray Donnelly,