Merge #1639

1639: Add FAQ entry for how to use webdav(radicale) r=mergify[bot] a=Diman0

## What type of PR?

documentation

## What does this PR do?

Add faq entry for how to use webdav (radicale). 

### Related issue(s)
- Auto close an issue like: closes #1591

## Prerequistes
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.

- [x] In case of feature or enhancement: documentation updated accordingly
- [n/a] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.


Co-authored-by: Dimitri Huisman <diman@huisman.xyz>

docs/faq.rst

@@ -327,6 +327,24 @@ After successfull login the domain part will be striped and the rest used as use
 
 *Issue reference:* `575`_.
 
+
+How do I use webdav (radicale)?
+```````````````````````````````
+
+| For first time set up, the user must access radicale via the url `https://mail.example.com/webdav/.web` and then
+| 1. Log in using the  user's full email address and password.
+| 2. Click 'Create new addressbook or calendar'
+| 3. Follow instructions for creating an addressbook (for contact management) and calendar.
+|
+| Subsequently to use webdav (radicale), you can configure your carddav/caldav client to use the following url:
+| `https://mail.example.com/webdav/user@example.com`
+| As username you must provide the complete email address (user@example.com).  
+| As password you must provide the password of the email address.
+| The user must be an existing Mailu user.
+
+*issue reference:* `1591`_.
+
+
 .. _`Postfix`: http://www.postfix.org/postconf.5.html
 .. _`Dovecot`: https://doc.dovecot.org/configuration_manual/config_file/config_file_syntax/
 .. _`NGINX`:   https://nginx.org/en/docs/
@@ -342,6 +360,7 @@ After successfull login the domain part will be striped and the rest used as use
 .. _`520`: https://github.com/Mailu/Mailu/issues/520
 .. _`591`: https://github.com/Mailu/Mailu/issues/591
 .. _`575`: https://github.com/Mailu/Mailu/issues/575
+.. _`1591`: https://github.com/Mailu/Mailu/issues/1591
 
 Technical issues
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