Rename of README to README.md causes make errors

[garybuhrmaster]

As of commit f987fc75266 ("Renamed README -> README.md and amended for markdown support.") a (unix) perl Makefile.PL will result in the message:

Warning: the following files are missing in your kit:
README
Please inform the author.

followed by a make which results in the message:

make: *** No rule to make target 'README', needed by 'blib/doc/README'.  Stop.

Proposed patch follows:

diff --git a/MANIFEST b/MANIFEST
index 4c8578d6..c654700d 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -29,7 +29,7 @@ COPYING
 Changes
 MANIFEST
 Makefile.PL
-README
+README.md
 README.cygwin
 Uninstall.pm
 authors.txt
diff --git a/Makefile.PL b/Makefile.PL
index ea0bd7bf..9dfc989f 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -92,7 +92,7 @@ our %extra_constants;
 # because it is accessed by some code we add to MakeMaker.
 #
 our @docs;
-@docs = qw(doc/COPYING doc/QuickStart doc/README.win32 README);
+@docs = qw(doc/COPYING doc/QuickStart doc/README.win32 README.md);

 # Executables to be installed.
 my @exes