[PATCH] Docs: fix explanation of file-nr

Patch from Paul Jakma <paulj@alphyra.ie>

Documentation/sysctl/fs.txt is incorrect wrt to the middle number of
/proc/sys/fs/file-nr.  The current docs state it is the number of
in-use file-handles, from observation this number is actually the
number of /unused/ file-handles - we've observe that when it hits 0 we
get file handle problems (rather than when it hits == file-max as docs
imply).

Documentation/sysctl/fs.txt

@@ -82,11 +82,11 @@ of error messages about running out of file handles, you might
 want to increase this limit.
 
 The three values in file-nr denote the number of allocated
-file handles, the number of used file handles and the maximum
+file handles, the number of unused file handles and the maximum
 number of file handles. When the allocated file handles come
-close to the maximum, but the number of actually used ones is
-far behind, you've encountered a peak in your usage of file
-handles and you don't need to increase the maximum.
+close to the maximum, but the number of unused file handles is
+significantly greater than 0, you've encountered a peak in your 
+usage of file handles and you don't need to increase the maximum.
 
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