Link the old RPM cache install doc to the new RPM cache install doc

docs/data/stashcache/install-cache.md

@@ -6,7 +6,9 @@ Installing the OSDF Cache
 
 !!! warning "Deprecation warning"
     This document is outdated and describes an XCache-based OSDF Cache install, which is deprecated.
-    Future OSDF Caches should be based on Pelican; documentation for a Pelican-based OSDF Cache install is forthcoming.
+    Future OSDF Caches should be based on Pelican.
+
+    See the [Pelican-based Installing the OSDF Cache by RPM](../../osdf/install-cache-rpm) document
 
 This document describes how to install an Open Science Data Federation (OSDF) cache service.  This service allows a site or regional
 network to cache data frequently used on the OSG, reducing data transfer over the wide-area network and