docs: move /var/log/README to a tmpfiles.d symlink

This moves the /var/log/README content out of /var and into the
docs location, replacing the previous file with a symlink
created through a tmpfiles.d entry.

docs/var-log/meson.build

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
 if conf.get('HAVE_SYSV_COMPAT') == 1 and get_option('create-log-dirs')
-        install_data('README',
-                     install_dir : '/var/log')
+        install_data('README.logs',
+                     install_dir : docdir)
 endif