docs: add service readme file

docs/polygon.md

@@ -0,0 +1,21 @@
+<h1 align="center">Polygon.io Agentic Service</h1>
+
+## Intro
+
+[Polygon.io][polygon] is a powerful stock market data API provider that provides extensive APIs that range from the realtime and historical data on stocks, options, indices, forex, crypto. Built for developers by developers, Polygon.io is the ideal data provider for your next project.
+
+## Pre-requisites
+
+Ensure the following environment variable is set:
+
+- `POLYGON_API_KEY` - API key for Polygon.io.
+
+Otherwise, you can pass it in as an argument to the `PolygonClient ` constructor.
+
+### How to Retrieve API Key
+
+1. Open [Polygon.io][polygon] and sign up for an account or log in.
+2. On the left side of the screen, click on the `API Keys` menu item.
+3. Locate your API key and copy it to your clipboard by clicking on the respective button.
+
+[polygon]: https://polygon.io

src/services/polygon.ts

@@ -831,6 +831,11 @@ export interface PolygonExchange {
   url?: string
 }
 
+/**
+ * Client for the Polygon.io REST API.
+ *
+ * @see {@link https://polygon.io/docs}
+ */
 export class PolygonClient {
   /**
    * HTTP client for the Polygon API.