Add mainnet connection docs (#88)

Author: calummoore

get-started.mdx

@@ -118,7 +118,7 @@ await db.collection("City").create(["new-york", "New York"]);
 
 You can update records by calling methods defined on your collection.
 
-```js
+```typescript
 import { Polybase } from "@polybase/client";
 
 const db = new Polybase({ defaultNamespace: "your-namespace" });

mainnet.mdx

@@ -0,0 +1,21 @@
+---
+title: "Private Mainnet"
+---
+
+The Polybase Mainnet is currently invite-only. If you have a production use case and would like to join the private mainnet, please [apply here](https://ask.polybase.xyz/mainnet).
+
+## Configuring the SDK
+
+To connect to the Polybase Mainnet, you will need to configure the SDK with the following parameters:
+
+```typescript
+import { Polybase } from "@polybase/client";
+
+const db = new Polybase({ 
+  baseURL: "https://mainnet.polybase.xyz/v0",
+  defaultNamespace: "your-namespace" 
+});
+
+// Now you can use the SDK as normal
+await db.collection("City").call("setCountry", ["USA"]);
+```

mint.json

@@ -72,6 +72,7 @@
         "react",
         "faq",
         "upgrading",
+        "mainnet",
         "how-it-works",
         "known-issues",
         "indexers",