patch 8.2.4249: the timeout limit for spell suggestions is always 5000

Problem:    The timeout limit for spell suggestions is always 5000 milli
            seconds.
Solution:   Add the "timeout" entry to 'spellsuggest'.
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 55e3cf8..199c261 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -7363,6 +7363,12 @@
 			suggestions is never more than the value of 'lines'
 			minus two.
 
+	timeout:{millisec}   Limit the time searching for suggestions to
+			{millisec} milli seconds.  Applies to the following
+			methods.  When omitted the limit is 5000. When
+			negative there is no limit.  {only works when built
+			with the +reltime feature}
+
 	file:{filename} Read file {filename}, which must have two columns,
 			separated by a slash.  The first column contains the
 			bad word, the second column the suggested good word.