Tidy docs for Device API

Signed-off-by: Tim Bannister <tim@scalefactory.com>

docs/device-api.md

@@ -1,21 +1,24 @@
 # Device
 
-The Device-API following functionality matrix indicates which devices are
+Firecracker provides the _Device_ API to let you manage the virtual hardware
+available inside each microVM.
+
+The Device API following functionality matrix indicates which devices are
 required for an API call to be usable.
 
 **O** - Optional: The device (column) **is not required** for a Firecracker
-microVM API call to succeed. If the device (column) is omitted from a uVM
+microVM API call to succeed. If the device (column) is omitted from a μVM
 definition, a call to one of the [API Endpoints](#api-endpoints) will succeed.
 
 **R** - Required: The device (column) **is required** for a Firecracker microVM
-API call to succeed. If the device (column) is omitted from a uVM definition,
+API call to succeed. If the device (column) is omitted from a μVM definition,
 a call to one of the [API Endpoints](#api-endpoints) will return a result that
 depends on the device (see [issue #2173](https://github.com/firecracker-microvm/firecracker/issues/2173)).
 
-- API calls related to `drives/{id}` result in 400 - BadRequest - HTTP response
+- API calls related to `drives/{id}` result in 400 - Bad Request - HTTP responses
   if the block device identified by `id` was not previously configured.
 - API calls related to `network-interfaces/{id}` result in 400 - BadRequest -
-  HTTP response if the network device identified by `id` was not previously
+  HTTP responses if the network device identified by `id` was not previously
   configured.
 
 ## API Endpoints