Add MAkefile.* to EXTRA_DIST to ensure they end up in tarballs

Change-Id: Ibbae061fda3db49f8ecda263cfc3ca6873c0b1b3
diff --git a/Makefile.am b/Makefile.am
index 960ca07..12a9a82 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -3,3 +3,5 @@
 
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = libgtp.pc
+
+EXTRA_DIST = README README.FreeBSD README.MacOSX README.Solaris