Rename INSTALL to INSTALL.md, so that GitLab renders it more nicely.

refs: #11262

Makefile.am

 # vi: noexpandtab softtabstop=0
 ## Process this file with automake to produce Makefile.in
 
-EXTRA_DIST = FAQ README.md COPYING AUTHORS INSTALL NEWS ChangeLog \
+EXTRA_DIST = FAQ README.md COPYING AUTHORS INSTALL.md NEWS ChangeLog \
              backupninja.spec backupninja.spec.in autogen.sh
 
 SUBDIRS = etc examples handlers lib man src

backupninja.spec.in

@@ -50,7 +50,7 @@ rm -fr %{buildroot}
 
 %ghost %{_localstatedir}/log/backupninja.log
 
-%doc AUTHORS COPYING ChangeLog INSTALL NEWS README.md
+%doc AUTHORS COPYING ChangeLog INSTALL.md NEWS README.md
 %{_mandir}/man1/*
 %{_mandir}/man5/*