Merge remote-tracking branch 'origin/master' into master-next

Author: swift-ci

README.md

@@ -54,7 +54,7 @@ discussed below.
 macOS, Ubuntu Linux LTS, and the latest Ubuntu Linux release are the current
 supported host development operating systems.
 
-For macOS, you need [Xcode 9.0 beta 1](https://developer.apple.com/xcode/downloads/).
+For macOS, you need [Xcode 9.0 beta 2](https://developer.apple.com/xcode/downloads/).
 
 For Ubuntu, you'll need the following development dependencies:
 
@@ -101,11 +101,11 @@ command line tools to your `PATH`:
 
 #### Ninja
 [Ninja](https://ninja-build.org) is the current recommended build system
-for building Swift and is the default configuration generated by CMake. If
-you're on macOS or don't install it as part of your Linux distribution, clone
-it next to the other projects and it will be bootstrapped automatically:
+for building Swift and is the default configuration generated by CMake. [Pre-built
+packages](https://github.com/ninja-build/ninja/wiki/Pre-built-Ninja-packages)
+are available for macOS and Linux distributions. You can also clone Ninja
+next to the other projects and it will be bootstrapped automatically:
 
-##### Build from source
 **Via HTTPS**
 
     git clone https://github.com/ninja-build/ninja.git && cd ninja