Add build instructions for MacPorts

Mac users use Homebrew or MacPorts to get their "unix" tools. 

Add instructions to build on MacPorts users.

Signed-off-by: Amit Kucheria <[email protected]>

Author: idlethread

README.md

@@ -17,11 +17,18 @@ make
 
 ### MacOS
 
+For Homebrew users,
 ```bash
 brew install libxml2 pkg-config libusb
 make
 ```
 
+For MacPorts users
+```bash
+sudo port install libxml2 pkgconfig libusb
+make
+```
+
 ### Windows
 
 First, install the [MSYS2 environment](https://www.msys2.org/). Then, run the