17159 fix plugin install instructions

netbox/templates/core/inc/plugin_installation.html

@@ -18,8 +18,8 @@ PLUGINS=［
 <p>3. Still from the NetBox virtual environment, run database migrations and collect static files:</p>
 
 <pre class="block">
-python3 /opt/netbox/netbox/netbox/manage.py migrate
-python3 /opt/netbox/netbox/netbox/manage.py collectstatic
+python3 /opt/netbox/netbox/manage.py migrate
+python3 /opt/netbox/netbox/manage.py collectstatic
 </pre>
 
 <p>4. Restart the NetBox services to complete the plugin installation:</p>