Documented the exchange interface.

src/index.ts

@@ -1,9 +1,23 @@
 import { PortfolioProvider } from "./interface/portfolio";
 import { QuoteProvider } from "./interface/quote";
 
+/**
+ * Represents an exchange, which provides access to a portfolio provider and a quote provider.
+ */
 export interface Exchange {
+
+    /**
+     * The portfolio provider for the exchange.
+     */
     readonly portfolioProvider: PortfolioProvider;
+
+    /**
+     * The quote provider for the exchange.
+     */
     readonly quoteProvider: QuoteProvider;
 
+    /**
+     * The name of the exchange.
+     */
     readonly name: string;
-}
+}