docs: move API.md to root dir (#1050)

* refactor: move API to root dir

* fix: broken API link in readme

README.md

@@ -101,7 +101,7 @@ All autocollection is on by default. By using the full version of the JavaScript
 ### Telemetry Initializers
 Telemetry initializers are used to modify the contents of collected telemetry before being sent from the user's browser. They can also be used to prevent certain telemetry from being sent, by returning `false`. Multiple telemetry initializers can be added to your Application Insights instance, and they are executed in order of adding them.
 
-The input argument to `addTelemetryInitializer` is a callback that takes a [`ITelemetryItem`](./API.md#addTelemetryInitializer) as an argument and returns a `boolean` or `void`. If returning `false`, the telemetry item is not sent, else it proceeds to the next telemetry initializer, if any, or is sent to the telemetry collection endpoint.
+The input argument to `addTelemetryInitializer` is a callback that takes a [`ITelemetryItem`](./API-reference.md#addTelemetryInitializer) as an argument and returns a `boolean` or `void`. If returning `false`, the telemetry item is not sent, else it proceeds to the next telemetry initializer, if any, or is sent to the telemetry collection endpoint.
 
 An example of using telemetry initializers:
 ```ts