Revert adding reStructuredText extension to README

This reverts commits fbf77f58 and
3816e401.

While having the .rst extension helps GitHub formatting the file, the
renaming broke both Autotools and Waf build systems.

Makefile.am

@@ -36,7 +36,6 @@ EXTRA_DIST = \
 	geany.gladep \
 	ChangeLog.pre-0-17 \
 	HACKING \
-	README.rst \
 	README.I18N \
 	README.Packagers \
 	po/intl_stats.sh \

configure.ac

@@ -6,7 +6,7 @@ AC_INIT([Geany], [1.22],
 AC_CONFIG_SRCDIR([src/geany.h])
 AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_MACRO_DIR([m4])
-AM_INIT_AUTOMAKE([foreign])
+AM_INIT_AUTOMAKE
 AC_CONFIG_HEADERS([config.h])
 
 m4_ifdef([AM_SILENT_RULES],[AM_SILENT_RULES([yes])])