state in readme that we support HTTP/2 and how to disable it

Author: dnadoba

Diff for: README.md

@@ -7,6 +7,7 @@ This library provides the following:
 3. Streaming body download
 4. TLS support
 5. Cookie parsing (but not storage)
+6. Automatic HTTP/2 over HTTPS (since version 1.7.0)
 
 ---
 
@@ -216,7 +217,7 @@ httpClient.execute(
 ).whenComplete (...)
 ```
 
-Direct URLs can easily be contructed to be executed in other scenarios:
+Direct URLs can easily be constructed to be executed in other scenarios:
 ```swift
 let socketPathBasedURL = URL(
     httpURLWithSocketPath: "/tmp/myServer.socket", 
@@ -228,6 +229,17 @@ let secureSocketPathBasedURL = URL(
 )
 ```
 
+### Disabling HTTP/2
+The exclusive use of HTTP/1 is possible by setting `httpVersion` to `.http1Only` on `HTTPClient.Configuration`:
+```swift
+var configuration = HTTPClient.Configuration()
+configuration.httpVersion = .http1Only
+let client = HTTPClient(
+    eventLoopGroupProvider: .createNew,
+    configuration: configuration
+)
+```
+
 ## Security
 
 Please have a look at [SECURITY.md](SECURITY.md) for AsyncHTTPClient's security process.