squid / WPAD: Add Wiki-Link for required further adjustments to GUI

squid / WPAD: Add Wiki-Link for required further adjustments to GUI

This patch adds a notice with a link to the Wiki-page https://wiki.ipfire.org/configuration/network/proxy/extend/wpad to the new WebGUI-Setion to make the user aware of the fact, that WPAD will only work correctly if he makes further adjustments:

- Add DHCP-Options for WPAD via DHCP
- Add HOST-Entries to DNS and Apache-vhost or haproxy-frontend/backend or firewall-redirect for WPAD via DNS

These additional options depend on the users environment and can not be shipped by default as they might break the users setups.

Note: The translations are only done for "en" and "de" yet!

Signed-off-by: Alexander Koch <ipfire@starkstromkonsument.de>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>