binutils/doc: Update documentation for nm --size-sort

The documentation for 'nm --size-sort' is out of step with the code, the
special handling for ELF is not mentioned in the documentation, and
could cause confusion to a user.

binutils/ChangeLog:

	* doc/binutils.texi (nm): Update description of --size-sort.

binutils/ChangeLog

+2016-05-10  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* doc/binutils.texi (nm): Update description of --size-sort.
+
 2016-05-09  Nick Clifton  <nickc@redhat.com>
 
 	PR binutils/20063

binutils/doc/binutils.texi

@@ -1012,11 +1012,12 @@ types.  This option is only available if the toolchain has been built
 with plugin support enabled.
 
 @item --size-sort
-Sort symbols by size.  The size is computed as the difference between
-the value of the symbol and the value of the symbol with the next higher
-value.  If the @code{bsd} output format is used the size of the symbol
-is printed, rather than the value, and @samp{-S} must be used in order
-both size and value to be printed.
+Sort symbols by size.  For ELF objects symbol sizes are read from the
+ELF, for other object types the symbol sizes are computed as the
+difference between the value of the symbol and the value of the symbol
+with the next higher value.  If the @code{bsd} output format is used
+the size of the symbol is printed, rather than the value, and
+@samp{-S} must be used in order both size and value to be printed.
 
 @item --special-syms
 Display symbols which have a target-specific special meaning.  These