fix: Update iOS version requirements

NOTE: This is not a breaking change, because the code hasn't fundamentally changed since the introduction of version 5.0.0, this is just a fix that makes version 5.0.0 work correctly.

Co-authored-by: Matic Zavadlal <matic.zavadlal@gmail.com>

Package.swift

@@ -1,11 +1,11 @@
-// swift-tools-version:5.6
+// swift-tools-version:5.7
 
 import PackageDescription
 
 let package = Package(
     name: "swift-graphql",
     platforms: [
-        .iOS(.v13),
+        .iOS(.v15),
         .macOS(.v10_15),
         .tvOS(.v13),
         .watchOS(.v6)

website/docs/README.mdx

@@ -19,6 +19,9 @@ The library is centered around three core principles:
 SwiftGraphQLClient is heavily inspired by `urql` GraphQL client in the JavaScript community. It models the queries as streams of values and lets you create custom operation processors called exchanges.
 
 ```swift
+import SwiftGraphQLClient
+import GraphQL
+
 let request = URLRequest(url: URL(string: "http://127.0.0.1:4000/graphql")!)
 let client = SwiftGraphQLClient.Client(request: request)