Docs for Siren (#4023)

This adds some documentation for the Siren app into the Lighthouse book.

Co-authored-by: Mavrik <mrricki.m.usmc@gmail.com>

book/src/ui-configuration.md

@@ -0,0 +1,47 @@
+# Configuration
+
+Siren requires a connection to both a Lighthouse Validator Client
+and a Lighthouse Beacon Node. Upon running you will first be greeted by the
+following configuration screen.
+
+![ui-configuration](./imgs/ui-configuration.png)
+
+
+## Connecting to the Clients
+
+This allows you to enter the address and ports of the associated Lighthouse
+Beacon node and Lighthouse Validator client.
+
+> The Beacon Node must be run with the `--gui` flag set. To allow the browser
+> to access the node beyond your local computer you also need to allow CORS in
+> the http API. This can be done via `--http-allow-origin "*"`.
+
+A green tick will appear once Siren is able to connect to both clients. You
+can specify different ports for each client by clicking on the advanced tab.
+
+
+## API Token
+
+The API Token is a secret key that allows you to connect to the validator
+client. The validator client's HTTP API is guarded by this key because it
+contains sensitive validator information and the ability to modify
+validators. Please see [`Validator Authorization`](./api-vc-auth-header.md)
+for further details. 
+
+Siren requires this token in order to connect to the Validator client.
+The token is located in the default data directory of the validator
+client. The default path is
+`~/.lighthouse/<network>/validators/api-token.txt`.
+
+The contents of this file for the desired valdiator client needs to be
+entered.
+
+## Name
+
+This is your name, it can be modified and is solely used for aesthetics. 
+
+## Device
+
+This is a name that can be associated with the validator client/beacon
+node pair. Multiple such pairs can be remembered for quick swapping between
+them.