doc: `path.relative` uses `cwd`

PR-URL: https://github.com/nodejs/node/pull/13714
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/path.md

@@ -445,9 +445,9 @@ changes:
 * `to` {string}
 * Returns: {string}
 
-The `path.relative()` method returns the relative path from `from` to `to`.
-If `from` and `to` each resolve to the same path (after calling `path.resolve()`
-on each), a zero-length string is returned.
+The `path.relative()` method returns the relative path from `from` to `to` based
+on the current working directory. If `from` and `to` each resolve to the same
+path (after calling `path.resolve()` on each), a zero-length string is returned.
 
 If a zero-length string is passed as `from` or `to`, the current working
 directory will be used instead of the zero-length strings.