doc: add formatting for version numbers to doc-style-guide.md

PR-URL: nodejs#33755
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/guides/doc-style-guide.md

@@ -65,6 +65,12 @@
 * For headings, use sentence case, not title case.
   * OK: _## Everybody to the limit_
   * NOT OK: _## Everybody To The Limit_
+* When referring to a version of Node.js in prose, use _Node.js_ and the version
+  number. Do not prefix the version number with _v_ in prose. This is to avoid
+  confusion about whether _v8_ refers to Node.js 8.x or the V8 JavaScript
+  engine.
+  * OK: _Node.js 14.x_, _Node.js 14.3.1_
+  * NOT OK: _Node.js v14_
 
 See also API documentation structure overview in [doctools README][].