docs: clarify version field can be omitted in package-lock

Author: Max Black

docs/lib/content/configuring-npm/package-lock-json.md

@@ -136,6 +136,7 @@ npm v7 ignores this section entirely if a `packages` section is present, but doe
 Dependency objects have the following fields:
 
 * version: a specifier that varies depending on the nature of the package, and is usable in fetching a new copy of it.
+  Note that for peer dependencies that are not installed, or optional dependencies that are not installed, this field may be omitted.
 
     * bundled dependencies: Regardless of source, this is a version number that is purely for informational purposes.
     * registry sources: This is a version number.