Update build instructions.

README.md

@@ -68,10 +68,14 @@ For more information, please visit the
 
 ## Building
 
-Simply run `./cake` (a [Bash](https://www.gnu.org/software/bash) script) to
-build artifacts. This will use the `Debug` configuration by default, which is
-suitable for development and debugging. Pass `-c Release` instead to use that
-configuration, resulting in an optimized build.
+You will need the .NET SDK installed. Simply run `./cake`
+(a [Bash](https://www.gnu.org/software/bash) script) to build artifacts. You can
+also use `./cake pack` if you do not want to build the documentation (which
+requires Node.js).
+
+These commands will use the `Debug` configuration by default, which is suitable
+for development and debugging. Pass `-c Release` instead to get an optimized
+build.
 
 ## License