Fix headings in connectivity.md

Update heading sizes and add unique heading ID for linking best practices and proper rendering.

Author: Amanda Butler

docs/reference/technology/connectivity/connectivity.md

@@ -1,20 +1,20 @@
-### Network connectivity in Mbed OS
+<h2 id="connectivity-tech">Network connectivity in Mbed OS</h2>
 
 Mbed OS supports a wide range of connectivity options. This section helps you to understand how to connect Mbed OS based devices to the outside world.
 
 <span class="images">![](https://s3-us-west-2.amazonaws.com/mbed-os-docs-images/connectivity.png)<span>Connectivity options</span></span>
 
 Below is a brief introduction of the different connectivity technologies that we support.
 
-#### Bluetooth low energy
+### Bluetooth low energy
 
 <span class="images">![](https://s3-us-west-2.amazonaws.com/mbed-os-docs-images/bluetooth.png)<span>Bluetooth</span></span>
 
 Bluetooth low energy (BLE) is a low power wireless technology standard for personal area networks. Typical applications of BLE are health care, fitness trackers, beacons, smart homes, security, entertainment, proximity sensors, industrial applications and automotives.
 
 To learn how to use Bluetooth low energy on Mbed OS, please refer to the [Bluetooth](/docs/development/reference/bluetooth.html) user API reference.
 
-#### IP Networking
+### IP Networking
 
 Arm Mbed OS supports various IP based connectivity options and IP stacks.
 
@@ -26,7 +26,7 @@ Mbed OS provides network drivers, such as Ethernet, Wi-Fi and cellular.
 
 You can find descriptions of supported interfaces and protocols in the [IP networking](/docs/development/reference/ip-networking.html) section.
 
-#### 6LoWPAN Mesh networking
+### 6LoWPAN Mesh networking
 
 <span class="images">![](https://s3-us-west-2.amazonaws.com/mbed-os-docs-images/mesh.png)<span>Tree type mesh</span></span>
 
@@ -36,7 +36,7 @@ Applications running on 6LoWPAN based mesh networks use the same Mbed OS Socket
 
 For descriptions of mesh networks, please see the [6LoWPAN Mesh](/docs/development/reference/technology.html) section.
 
-#### LoRa
+### LoRa
 
 <span class="images">![](https://s3-us-west-2.amazonaws.com/mbed-os-docs-images/lora.png)<span>LoRa</span></span>