Add HTTPS documentation

docs/basics/foris-https/https.md

+# Accessing Foris via HTTPS
+
+If you see warning box bellow in your Foris web interface, you should add a
+permanent certificate exception in your browser. Read on to find out what the
+warning means and how to add the permanent certificate exception to suppress
+this warning.
+
+![Warning](warning.png)
+
+## What does this warning mean?
+
+In order to safely configure your router, you need a secure channel.  If you
+don't want to use just your ethernet cable to connect to your router, **a safe
+way is to use HTTPS**. Why is HTTPS safe? For one, HTTPS requires a **trusted
+certificate** and if the certificate is not trusted, then warnings are
+displayed. We use **self-signed certificates**, which are generated on
+factory-reset and cannot, unfortunately, be trusted before the first visit to
+Foris and it is recommended to **add a permanent exception in your browser**
+for the certificate to be trusted in future connections.
+
+## More about warnings
+
+!!! warning
+    Do not blindly skip untrusted certificate errors. There are there for a
+    good reason and might be indication of an attack attempt.
+
+Generally, if a warning is displayed on the web page where you happen to be,
+**do not proceed!** It is possible that someone simply misconfigured the web
+server but there could also be an **ongoing attack**. In case this happens, use
+a different device or browser. If that doesn't help, use a different channel to
+configure your router or wait for a bit. A few minutes are **not worth your
+passwords, card number or any other data!** If you decide to continue to the
+web page, you should know exactly what you are doing. Adding the exception for
+Foris is one of a little cases where this way is suitable.
+
+## Adding a permanent exception
+
+The certificate is generated on factory reset so you need to add or change the
+exception each time you take the router back to factory settings.
+
+!!! tip
+    We strongly recommend to use Mozilla Firefox for configuration of your
+    Turris because it has the simplest process to save the exception.
+    Furthermore it is a free browser (free both as in speech and as in beer),
+    it is secure, easily extendable by plugins and is available on all common
+    platforms.
+
+Here is the guide for Mozilla Firefox on any platform (as of the version 67
+released in May 2019):
+
+1. When you open the Foris page for the first time this warning is displayed:
+
+![Firefox: Security warning](firefox-01.png)
+
+2. Press the _Advanced..._ button to display more details:
+
+![Firefox: Advanced options](firefox-02.png)
+
+3. Press the _Accept the Risk and Continue_ button now. The exception is
+   saved and the browser will no longer show the warning text.

mkdocs.yml

@@ -59,6 +59,7 @@ nav:
         - 'What we collect': 'basics/collect/data.md'
         - 'How to setup?': 'basics/collect/howto.md'
     - Foris:
+        - 'Secure access': 'basics/foris-https/https.md'
         - LAN: 'basics/foris-lan/foris-lan.md'
         - WAN: 'basics/foris-wan/foris_wan.md'
         - DNS: 'basics/foris-dns/foris-dns.md'