Add docs for NINA warning filters (#28586)

* Add docs for filters

* tiny tweaks

---------

Co-authored-by: c0ffeeca7 <[email protected]>

source/_integrations/nina.markdown

@@ -20,6 +20,40 @@ For each county/city it creates warning slots that change to Unsafe when warning
 
 {% include integrations/config_flow.md %}
 
+### Filter
+
+The integration includes the possibility to filter warnings in two ways via a regex.
+
+<div class='note'>
+All filters are applied to lowercase text only.
+</div>
+
+#### Headline filter
+
+This filter filters warnings based on the headline as a **blacklist**. In other words, if the regular expression matches the headline of the warning, the warning will be **ignored**.
+
+Default: Match nothing (`/(?!)/`)
+
+##### Example
+
+Ignore warnings that contain the word `corona`
+
+Regex: `.*corona.*` <br>
+Headline: `corona-verordnung des landes: warnstufe durch landesgesundheitsamt ausgerufen`
+
+#### Affected area filter
+
+This filter **whitelists** warnings based on the affected area. In other words, if the regular expression matches the area, the warning will be **displayed**.
+
+Default: Match all (`.*`)
+
+##### Example
+
+Show only warnings from the city of nagold.
+
+Regex: `.*nagold.*` <br>
+Areas: `gemeinde oberreichenbach, gemeinde neuweiler, stadt nagold`
+
 ### Attributes
 
 | Attribute    | Description                            |
@@ -28,6 +62,8 @@ For each county/city it creates warning slots that change to Unsafe when warning
 | `description` | *(str)* Official description of the warning. |
 | `sender` | *(str)* Sender of the warning. Can be empty. |
 | `severity` | *(str)* Severity of the warning. <br>Extreme - Extraordinary threat to life or property <br>Severe - Significant threat to life or property <br>Moderate - Possible threat to life or property <br>Minor – Minimal to no known threat to life or property <br>Unknown - Severity unknown |
+| `recommended_actions` | *(str)* The recommendations for action. |
+| `affected_areas` | *(str)* Areas where the warning applies. |
 | `id` | *(str)* Individual ID for each warning. |
 | `sent` | *(time)* Transmission time and date (UTC) of the issued warning. |
 | `start` | *(time)* Starting time and date (UTC) of the issued warning. Can be empty. |