api-parse-options.txt: document "no-" for non-boolean options

Document that the "no-" prefix can also be used for non-boolean
options.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-parse-options.txt

@@ -41,6 +41,8 @@ The parse-options API allows:
 * Boolean long options can be 'negated' (or 'unset') by prepending
   `no-`, e.g. `--no-abbrev` instead of `--abbrev`. Conversely,
   options that begin with `no-` can be 'negated' by removing it.
+  Other long options can be unset (e.g., set string to NULL, set
+  integer to 0) by prepending `no-`.
 
 * Options and non-option arguments can clearly be separated using the `--`
   option, e.g. `-a -b --option -- --this-is-a-file` indicates that