link reference docs and faq about BORG_FILES_CACHE_TTL, fixes #1561

docs/faq.rst

@@ -356,6 +356,8 @@ those files are reported as being added when, really, chunks are
 already used.
 
 
+.. _always_chunking:
+
 It always chunks all my files, even unchanged ones!
 ---------------------------------------------------
 

docs/usage.rst

@@ -89,6 +89,7 @@ General:
     BORG_FILES_CACHE_TTL
         When set to a numeric value, this determines the maximum "time to live" for the files cache
         entries (default: 20). The files cache is used to quickly determine whether a file is unchanged.
+        The FAQ explains this more detailled in: :ref:`always_chunking`
     TMPDIR
         where temporary files are stored (might need a lot of temporary space for some operations)