State cache.files per-process behaviour w/out match

This makes it clear, along with the previous commit, that per-process will allow
us to use parallel direct writes as they will mount with the equivalent
of cache.files=off (i.e. direct_io)

README.md

@@ -1294,12 +1294,12 @@ https://en.wikipedia.org/wiki/Page_cache
   unchanged since previous open.
 * cache.files=libfuse: follow traditional libfuse `direct_io`,
   `kernel_cache`, and `auto_cache` arguments.
-* cache.files=per-process: Enable page caching only for processes
-  which 'comm' name matches one of the values defined in
-  `cache.files.process-names`.
+* cache.files=per-process: Enable page caching (equivalent to `cache.files=partial`) 
+  only for processes which 'comm' name matches one of the values defined in
+  `cache.files.process-names`. If the name does not match the file open
+  is equivalent to `cache.files=off`.
 
-FUSE, which mergerfs uses, offers a number of page caching
-modes. mergerfs tries to simplify their use via the `cache.files`
+FUSE, which mergerfs uses, offers a number of page caching modes. mergerfs tries to simplify their use via the `cache.files`
 option. It can and should replace usage of `direct_io`,
 `kernel_cache`, and `auto_cache`.