Module chapter rewrite (nushell#1597)

* Module chapter rewrite

* Small tweaks while writing PR notes

* Fix typos

Author: NotTheDr01ds

.vuepress/configs/sidebar/en.ts

@@ -51,7 +51,15 @@ export const sidebarEn: SidebarConfig = {
         '/book/variables.md',
         '/book/control_flow.md',
         '/book/scripts.md',
-        '/book/modules.md',
+        {
+          text: 'Modules',
+          link: '/book/modules.md',
+          collapsible: false,
+          children: [
+            '/book/modules/using_modules.md',
+            '/book/modules/creating_modules.md',
+          ],
+        },
         '/book/overlays.md',
         '/book/testing.md',
         '/book/style_guide.md',
@@ -145,6 +153,7 @@ export const sidebarEn: SidebarConfig = {
         '/cookbook/foreign_shell_scripts',
         '/cookbook/pattern_matching',
         '/cookbook/external_completers',
+        '/cookbook/modules',
         '/cookbook/files',
         '/cookbook/git',
         '/cookbook/parsing_git_log',