Replace "restart shell" documentation "exec zsh" (#8411)

Running `source ~/.zshrc` can have side effects, it's better to reload the whole 
zsh session with `exec zsh`.

plugins/dircycle/README.md

@@ -15,10 +15,10 @@ This plugin enables directory navigation similar to using back and forward on br
    )
    ```
 
-2. Reload the source file or restart your Terminal session:
+2. Restart the shell or restart your Terminal session:
 
    ```console
-   $ source ~/.zshrc
+   $ exec zsh
    $
    ```