Work on "permissions" article [skip ci]

Author: jennybc

_pkgdown.yml

@@ -20,12 +20,15 @@ navbar:
       href: articles/articles/file-identification.html
     - text: Dealing with multiple files
       href: articles/articles/multiple-files.html
+    - text: File permissions
+      href: articles/articles/permissions.html
 
 articles:
   - title: "Articles"
     contents:
     - file-identification
     - multiple-files
+    - permissions
 
 reference:
   - title: "Reach out and touch your files"