added non-VM installation instructions

README

@@ -5,6 +5,28 @@ label the commands that potentially require network access, though this
 tutorial can be run completely self-contained on any Posix-compatible host with
 git installed.
 
+Installation
+============
+
+On your VM, git is already installed. The remainder of this section
+is for when you want to install git on another machine. We recommend
+having git installed on your laptop or desktop computer.
+
+If you're on a Linux system, then it's somewhat likely that git is
+already installed; if not, you can use your favorite package manager
+to install it. Don't forget to install the documentation, if it's
+in a separate package!
+
+If you're using MacOS, you have some options:
+ 1) Download and install git from https://git-scm.com/download/mac
+ 2) If you're using Homebrew, "brew install git git-sh" (search for
+    "git" to see other potentially useful packages)
+ 3) MacPorts also has a git package
+
+If you're using Windows, you can download the git installer from
+ - https://git-scm.com/download/win
+This includes both a GUI and a git bash shell.
+
 Basic Git Operations
 ====================