doc(man): clarify --path influnce on target-dir

Author: weihanglo

src/doc/man/includes/options-target-dir.md

@@ -3,7 +3,11 @@ Directory for all generated artifacts and intermediate files. May also be
 specified with the `CARGO_TARGET_DIR` environment variable, or the
 `build.target-dir` [config value](../reference/config.html).
 {{#if temp-target-dir}} Defaults to a new temporary folder located in the
-temporary directory of the platform.
+temporary directory of the platform. 
+
+When using `--path`, by default it will use `target` directory in the workspace
+of the local crate unless `--target-dir`
+is specified.
 {{else}} Defaults to `target` in the root of the workspace.
 {{/if}}
 {{/option}}