Fixed grammatical error.

Signed-off-by: TaikiYamada4 <taiki.yamada@tier4.jp>

docs/contributing/coding-guidelines/ros-nodes/directory-structure.md

@@ -4,7 +4,7 @@ This document describes the directory structure of ROS nodes within Autoware.
 
 We'll use the package `autoware_gnss_poser` as an example.
 
-**Note that this example does not reflect the actual `autoware_gnss_poser`, and has extra files and directories to demonstrate all possible package structure.**
+**Note that this example does not reflect the actual `autoware_gnss_poser` and includes extra files and directories to demonstrate all possible package structures.**
 
 ## C++ package