doc/muxers: Document problems of omitting nut syncpoints as well as alternatives

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/muxers.texi

@@ -714,6 +714,11 @@ Change the syncpoint usage in nut:
 @table @option
 @item @var{default} use the normal low-overhead seeking aids.
 @item @var{none} do not use the syncpoints at all, reducing the overhead but making the stream non-seekable;
+    Use of this option is not recommanded, as the resulting files are very damage
+    sensitive and seeking is not possible. Also in general the overhead from
+    syncpoints is negligible. Note, -@code{write_index} 0 can be used to disable
+    all growing data tables, allowing to mux endless streams with limited memory
+    and wihout these disadvantages.
 @item @var{timestamped} extend the syncpoint with a wallclock field.
 @end table
 The @var{none} and @var{timestamped} flags are experimental.