Fix markdownlint

Signed-off-by: Florian Hotze <florianh_dev@icloud.com>

developers/buildsystem.md

@@ -48,7 +48,7 @@ If the embedded bundle's manifest is not properly exporting all needed packages,
 In two cases using an "external" (i.e. not embedded) dependency is required:
 
 1. Dependencies to other openHAB bundles (e.g. `org.openhab.addons.bundles/org.openhab.binding.bluetooth/3.1.0-SNAPSHOT` or `org.openhab.addons.bundles/org.openhab.transform.map/3.1.0-SNAPSHOT`).
-2. Bundles that are used by more than one binding (e.g. Netty-bundles like `io.netty/netty-common/4.1.34.Final`).
+1. Bundles that are used by more than one binding (e.g. Netty-bundles like `io.netty/netty-common/4.1.34.Final`).
 
 Dependencies on other openHAB bundles should always have the scope `provided`.
 To ensure that external dependencies are available at runtime they also need to be added to the `feature.xml`:

mainui/CONTRIBUTING.md

@@ -28,6 +28,7 @@ Inside these comments, the UI allows the following features:
   ```markdown
   Add ... using the <!--F7:blue plus_circle_fill --> plus button ...
   ```
+
 - Link to UI pages by linking to
   - `.html` files inside this directory:<br>
     `[Items](items.html)` will navigate to `items/`.

mainui/settings/things.md

@@ -20,3 +20,11 @@ On this page, you can manage all the Things you have added to your system:
 - **Enable/Disable Things**<br>
   Select multiple Things using the top **Select** button and use the **Enable** or **Disable** buttons at the bottom or use the <!--F7 pause_circle --> pause button on the individual Thing pages.
 <!-- END MAINUI SIDEBAR DOC - DO NOT REMOVE -->
+
+## Inbox
+
+Many devices, technologies and systems can be automatically discovered on the network or browsed through some API.
+It therefore makes a lot of sense to use these features for a smart home solution.
+
+openHAB bindings can therefore implement Discovery Services for Things, which provide Discovery Results.
+All Discovery Results are put into the Thing inbox, from where they can be easily added to openHAB with just a few clicks.