Update links in build-osx.md

Add link to Github for Mac
Update link to HomeBrew

doc/build-osx.md

@@ -47,13 +47,13 @@ be done in `Xcode > Preferences > Downloads > Components` and generally must
 be re-done or updated every time Xcode is updated.
 
 There's an assumption that you already have `git` installed, as well. If
-not, it's the path of least resistance to install Github for Mac
+not, it's the path of least resistance to install [Github for Mac](https://mac.github.com/)
 (OS X 10.7+) or
 [Git for OS X](https://code.google.com/p/git-osx-installer/). It is also
 available via Homebrew or MacPorts.
 
-You will also need to install [Homebrew](http://mxcl.github.com/homebrew/)
-or [MacPorts](http://www.macports.org/) in order to install library
+You will also need to install [Homebrew](http://mxcl.github.io/homebrew/)
+or [MacPorts](https://www.macports.org/) in order to install library
 dependencies. It's largely a religious decision which to choose, but, as of
 December 2012, MacPorts is a little easier because you can just install the
 dependencies immediately - no other work required. If you're unsure, read