doc: v8 options can use either _ or -

This adds docs to the man page and online cli docs that v8 options can
be used with either dashes or underscores.

Refs: nodejs#6377 (comment)
PR-URL: nodejs#6532
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/cli.md

@@ -111,6 +111,10 @@ Process v8 profiler output generated using the v8 option `--prof`.
 
 Print v8 command line options.
 
+Note: v8 options allow words to be separated by both dashes (`-`) or underscores
+(`_`).
+
+For example, `--stack-trace-limit` is equivalent to `--stack_trace_limit`.
 
 ### `--tls-cipher-list=list`
 

doc/node.1

@@ -107,6 +107,12 @@ Process v8 profiler output generated using the v8 option \fB\-\-prof\fR
 .BR \-\-v8\-options
 Print v8 command line options.
 
+Note: v8 options allow words to be separated by both dashes (\fB-\fR) or
+underscores (\fB_\fR).
+
+For example, \fB\-\-stack\-trace\-limit\fR is equivalent to
+\fB\-\-stack\_trace\_limit\fR
+
 .TP
 .BR \-\-v8\-pool\-size =\fInum\fR
 Set v8's thread pool size which will be used to allocate background jobs.