Update readme with simple tutorial

Author: artemredkin

Diff for: README.md

@@ -1,3 +1,122 @@
 # swift-nio-http-client
+This package provides simple HTTP Client library built on top of SwiftNIO.
 
-Swift HTTP Client library built on top of SwiftNIO
+## Getting Started
+
+Add the following entry in your <code>Package.swift</code> to start using <code>HTTPClient</code>:
+
+### Swift 5
+
+```swift
+dependencies: [
+    .package(url: "https://github.com/swift-server/swift-nio-http-client.git", from: "1.0.0")
+]
+```
+
+## Status
+
+This library provides the following:
+1. Async single request methods
+2. Simple follow-redirect support (cookie headers are dropped)
+3. Body download streaming
+4. TLS support
+5. Cookie parsing (but not storage)
+
+## How to use
+
+### Request-Response API
+The code snippet below illustrates how to make a simple GET request to a remote server:
+
+```import HTTPClient
+
+let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
+let response = try httpClient.get(url: "https://swift.org").wait()
+
+if response.status == .ok {
+    // handle the response
+}
+
+// close the client
+try? httpClient.syncShutdown()
+```
+
+It is important to close client instance after use to cleanly shutdown underlying NIO ```EventLoopGroup```. Alternatively, you can provide shared ```EventLoopGroup```:
+```
+let httpClient = HTTPClient(eventLoopGroupProvider: .shared(userProvidedGroup))
+```
+In this case shutdown of the client is not neccecary.
+
+Library provides methods for most HTTP-methods. In case you need to have more control over the method, or you want to add headers or body, use ```HTTPRequest``` struct:
+```import HTTPClient
+
+let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
+defer {
+    try? httpClient.syncShutdown()
+}
+
+var request = try HTTPRequest(url: "https://swift.org", method: .POST)
+request.headers.add(name: "User-Agent", value: "Swift HTTPClient")
+request.body = .string("some-body")
+
+let response = try httpClient.execute(request: request).wait()
+
+if response.status == .ok {
+    // handle the response
+}
+```
+
+### Redirect following
+To enable follow-redirects behaviour, enable in using client configuration:
+```
+let httpClient = HTTPClient(eventLoopGroupProvider: .createNew,
+                            configuration: HTTPClientConfiguration(followRedirects: true))
+```
+
+### Timeouts
+Timeouts (connect and read) can be set in the client configuration:
+```
+let httpClient = HTTPClient(eventLoopGroupProvider: .createNew,
+                            configuration: HTTPClientConfiguration(timeout: Timeout(connectTimeout: .seconds(1),
+                                                                                    readTimeout: .seconds(1))))
+```
+or on per-request basis:
+```
+let response = try httpClient.execute(request: request, timeout: Timeout(connectTimeout: .seconds(1), readTimeout: .seconds(1))).wait()
+```
+
+### Streaming
+In case greater control over body processing is needed or you want to process HTTP Reponse body in a streaming manner, following delegate protocol could be used (example shows how to count bytes in response body without copiying it to the memory):
+```
+class CountingDelegate: HTTPResponseDelegate {
+    typealias Response = Int
+
+    var count = 0
+    
+    func didTransmitRequestBody() {
+        // this is executed when request is sent, called once
+    }
+
+    func didReceiveHead(_ head: HTTPResponseHead) {
+        // this is executed when we receive HTTP Reponse head part of the request (it contains response code and headers), called once
+    }
+
+    func didReceivePart(_ buffer: ByteBuffer) {
+        // this is executed when we receive parts of the response body, could be called zero or more times
+        count += buffer.readableBytes
+    }
+
+    func didFinishRequest() throws -> Int {
+        // this is called when request is fully read, called once, this is where you return a result or throw any errors you require to propagate to the client
+        return count
+    }
+    
+    func didReceiveError(_ error: Error) {
+        // this is called when we receive any network-related error, called once
+    }
+}
+
+let request = try HTTPRequest(url: "https://swift.org")
+let delegate = CountingDelegate()
+
+let count = try httpClient.execute(request: request, delegate: delegate).wait()
+```