a small suggestion to improve setafcl command

Author: garak

book/installation.rst

@@ -134,8 +134,8 @@ If there are any issues, correct them now before moving on.
 
     .. code-block:: bash
 
-        sudo setfacl -R -m u:www-data:rwx -m u:yourname:rwx app/cache app/logs
-        sudo setfacl -dR -m u:www-data:rwx -m u:yourname:rwx app/cache app/logs
+        sudo setfacl -R -m u:www-data:rwx -m u:`whoami`:rwx app/cache app/logs
+        sudo setfacl -dR -m u:www-data:rwx -m u:`whoami`:rwx app/cache app/logs
 
     **3. Without using ACL**