Document OS X dependency installation instructions

README.md

@@ -64,14 +64,6 @@ interface type 'Microsoft.Cci.ISymUnmanagedWriter5'`, please install
 
 [redist]: https://www.microsoft.com/en-hk/download/details.aspx?id=48145
 
-### OS X
-
-The OS X dependency installation instructions are not yet documented. You can
-try their PKG installer, or their [obtain script][]. We do not (yet) routinely
-test on OS X, but some developers use PowerShell on 10.10 and 10.11.
-
-[obtain script]: https://github.com/dotnet/cli/blob/rel/1.0.0/scripts/obtain/install.sh
-
 ## Building
 
 **The command `dotnet restore` must be done at least once from the top directory

docs/building/osx.md

@@ -0,0 +1,37 @@
+Build PowerShell on OS X
+========================
+
+This guide supplements the [Linux instructions](./linux.md), as
+building on OS X is almost identical.
+
+Please keep in mind that we do not yet routinely test on OS X, but
+some developers use PowerShell on 10.10 and 10.11.
+
+Environment
+===========
+
+You will want [Homebrew](http://brew.sh/), the missing package manager
+for OS X. Once installed, use `brew` to install the following
+dependencies.
+
+```sh
+brew install openssl cmake wget
+```
+
+Instead of using .NET CLI's Ubuntu package feed, you will want to use
+the official PKG installer.
+
+```sh
+wget https://dotnetcli.blob.core.windows.net/dotnet/beta/Installers/Latest/dotnet-dev-osx-x64.latest.pkg
+open ./dotnet-dev-osx-x64.latest.pkg
+```
+
+Then follow the wizard's instructions to complete installation.
+
+Build using our module
+======================
+
+Instead of installing the Ubuntu package of PowerShell, download the
+`pkg` from our GitHub releases page using your browser, complete the
+wizard, start a `powershell` session, and use `Start-PSBuild` from the
+module.