Instructions to install Ninja updated. (#10858)

* Instructions to install Ninja updated.

One sentence was not syntactically correct, I have replaced it to make the installation process clearer.

* Comma splice removed.

Author: armandgrillet

README.md

@@ -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