Add AppVeyor Build Status into README

Author: pali

README.pod

@@ -1,6 +1,17 @@
 =head1 DBD::MariaDB - database driver for Perl
 
-=for html <a href="https://travis-ci.org/gooddata/DBD-MariaDB"><img src="https://travis-ci.org/gooddata/DBD-MariaDB.svg?branch=master"></a>
+=begin html
+
+<p>
+<a href="https://travis-ci.org/gooddata/DBD-MariaDB/branches">
+<img src="https://travis-ci.org/gooddata/DBD-MariaDB.svg?branch=master"
+  alt="Travis CI Build Status"></a>
+<a href="https://ci.appveyor.com/project/gooddata/dbd-mariadb/branch/master">
+<img src="https://ci.appveyor.com/api/projects/status/github/gooddata/dbd-mariadb?branch=master&amp;svg=true"
+  alt="AppVeyor Build Status"></a>
+</p>
+
+=end html
 
 This is the Perl L<DBI> driver for access to MariaDB and MySQL databases.