Add info box (#3546)

* Add text on similarities between yaml and dicts

- Linewrapped the respective text to a with of 80 chars as well

* Adds reference to dicts/Hashtables when expl. YAML

- A comparison between dictionary/hastables and YAML is drawn
- Linewraps the paragraph to 80 characters

* Adds reference to python, indentation is mentioned

* Extends reasoning on YAMLLint

* Removes obsolete whitespace

* Fix whitespace

* Adds reference to inclusion of env-vars in YAML

* Add links

* Include note into the yaml explanation

- The YAMLLint stuff is a little off-topic, when raising the security
  concerns. It should hence go into an info box.

* Minor changes

source/_docs/configuration/yaml.markdown

@@ -30,8 +30,11 @@ The basics of YAML syntax are block collections and mappings containing key-valu
 
 Note that indentation (just like in Python) is an important part of specifying relationships using YAML. Things that are indented are nested "inside" things that are one level higher. So in the above example, `platform: pushbullet` is a property of (nested inside) the `notify` component.
 Getting the right indentation can be tricky if you're not using an editor with a fixed width font. Tabs are not allowed to be used for indentation. Convention is to use 2 spaces for each level of indentation.
-You can use the online service [YAMLLint](http://www.yamllint.com/) to check if your YAML syntax is correct before loading it into Home Assistant which will save you some time. If you do so, be aware that this is a third-party service and is not maintained by the Home Assistant community. *Please pay attention on not storing private data (passwords, api-keys, etc.) directly in that file.*
-Private data can be stored in a [seperate file](/docs/configuration/secrets/) or in [environmental variables](/docs/configuration/yaml/#using-environment-variables), which circumvents this problem of security.
+You can use the online service [YAMLLint](http://www.yamllint.com/) to check if your YAML syntax is correct before loading it into Home Assistant which will save you some time. If you do so, be aware that this is a thrid-party service and is not maintained by the Home Assistant community.
+
+<p class='note'>
+Please pay attention on not storing private data (passwords, API keys, etc.) directly in your `configuration.yaml` file. Private data can be stored in a [seperate file](/docs/configuration/secrets/) or in [environmental variables](/docs/configuration/yaml/#using-environment-variables), which circumvents this problem of security.
+</p>
 
 Text following a `#` are comments and are ignored by the system.