Complete DuckDNS add-on documentation (#749)

* Update README.md

* Update README.md

* Create README.md

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update duckdns/README.md

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update README.md

Additional fixes.

- Removed line separator from Option group `lets_encrypt`

* Delete README.md

* ✏️ Tweaks

duckdns/README.md

@@ -6,7 +6,7 @@ Automatically update your Duck DNS IP address with integrated HTTPS support via
 
 ## About
 
-[Duck DNS][duckdns] is a free service which will point a DNS (sub domains of duckdns.org) to an IP of your choice. This add-on includes support for Let’s Encrypt and will automatically create and renew your certificates. You will need to sign up for a Duck DNS account before using this add-on.
+[Duck DNS][duckdns] is a free service that will point a DNS (sub-domains of duckdns.org) to an IP of your choice. This add-on includes support for Let’s Encrypt and will automatically create and renew your certificates. You will need to sign up for a Duck DNS account before using this add-on.
 
 ## Installation
 
@@ -18,6 +18,13 @@ The installation of this add-on is straightforward and easy to do.
 
 ## How to use
 
+1. Visit [DuckDNS.org](https://www.duckdns.org/) and create an account by logging in through any of the available account services (Google, Github, Twitter, Persona).
+2. In the `Domains` section, type the name of the subdomain you wish to register and click `add domain`.
+3. If registration was a success, the subdomain is listed in the `Domains` section along with `current ip` being the public IP address of the device you are currently using to access `duckdns.org`. The IP address will be updated by the DuckDNS add-on.
+4. In the DuckDNS add-on configuration, perform the following:
+    - Copy the DuckDNS token (listed at the top of the page where account details are displayed) from `duckdns.org` and paste into the `token` option.
+    - Update the `domains` option with the full domain name you registered. E.g., `my-domain.duckdns.org`.
+
 
 ## Configuration
 
@@ -36,20 +43,46 @@ Add-on configuration:
 }
 ```
 
-### Option: `lets_encrypt`
+### Option group `lets_encrypt`
+
+The following options are for the option group: `lets_encrypt`. These settings
+only apply to Let's Encrypt SSL certificates.
+
+
+#### Option `lets_encrypt.accept_terms`
+
+Once you have read and accepted the Let's Encrypt [Subscriber Agreement](https://letsencrypt.org/repository/), change value to `true` in order to use Let's Encrypt services.
+
+
+#### Option `lets_encrypt.certfile`
+
+The name of the certificate file generated by Let's Encrypt. The file is used for SSL by Hass.io add-ons and is recommended to keep the filename as-is (`fullchain.pem`) for compatibility.
+
+**Note**: _The file is stored in `/ssl/`, which is the default for Hass.io_
+
+#### Option `lets_encrypt.keyfile`
+
+The name of the private key file generated by Let's Encrypt. The private key file is used for SSL by Hass.io add-ons and is recommended to keep the filename as-is (`privkey.pem`) for compatibility.
+
+**Note**: _The file is stored in `/ssl/`, which is the default for Hass.io_
 
 
 ### Option: `token`
 
+The DuckDNS authentication token found at the top of the DuckDNS account landing page. The token is required to make any changes to the subdomains registered to your account.
 
 ### Option: `domains`
 
+A list of DuckDNS subdomains registered under your account. An acceptable naming convention is `my-domain.duckdns.org`.
 
 ### Option: `seconds`
 
+The number of seconds to wait before updating DuckDNS subdomains and renewing Let's Encrypt certificates.
 
 ## Known issues and limitations
 
+- To log in, DuckDNS requires a free account from any of the following services: Google, Github, Twitter, or Persona.
+- A free DuckDNS account is limited to five subdomains.
 
 ## Support
 
@@ -61,7 +94,7 @@ You have several options to get them answered:
 - The Home Assistant [Community Forum][forum].
 - Join the [Reddit subreddit][reddit] in [/r/homeassistant][reddit]
 
-In case you've found an bug, please [open an issue on our GitHub][issue].
+In case you've found a bug, please [open an issue on our GitHub][issue].
 
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