Add resource under linux roadmap (#5608)

* add url to introductory resource

* Update src/data/roadmaps/linux/content/100-navigation-basics/103-directory-hierarchy.md

Co-authored-by: dsh <daniel.s.holdsworth@gmail.com>

* Update src/data/roadmaps/linux/content/100-navigation-basics/103-directory-hierarchy.md

---------

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>
Co-authored-by: dsh <daniel.s.holdsworth@gmail.com>

src/data/roadmaps/linux/content/100-navigation-basics/103-directory-hierarchy.md

@@ -4,4 +4,8 @@ In Linux, understanding the directory hierarchy is crucial for efficient navigat
 
 Each directory serves a specific purpose. For instance, `/bin` holds binary executable files (command files), `/etc` has system configuration files, `/home` stores users' personal files, and `/var` contains varying files such as logs and print queues.
 
-No code snippet is necessary as understanding directory hierarchy is a conceptual knowledge and doesn't involve code execution.
+No code snippet is necessary as understanding directory hierarchy is a conceptual knowledge and doesn't involve code execution.
+
+Visit the following resources to learn more:
+
+ - [Overview of File System Hierarchy Standard (FHS)](https://access.redhat.com/documentation/ru-ru/red_hat_enterprise_linux/4/html/reference_guide/s1-filesystem-fhs#s3-filesystem-usr).