doc: document behavior of `+timeout=T` when T<1
In case of T<1, timeout is set to 1 second.
$ time kdig example.cz @192.0.2.1 +timeout=0 +retry=0
;; WARNING: response timeout for 192.0.2.1@53(UDP)
;; ERROR: failed to query server 192.0.2.1@53(UDP)
real 0m1,013s
user 0m0,008s
sys 0m0,005s