Updates macOS section homebrew instructions

Just adding a basic workflow for getting bleeding-edge updates on homebrew which often lags due to it waiting for a new stable build .tar.gz to be generated.

COMPILING.txt

@@ -111,6 +111,28 @@ Latest non-stable from GitHub (use this if previous command fails)
 
 For more information go to https://github.com/iceman1001/homebrew-proxmark3
 
+Upgrading HomeBrew tap formula
+-----------------------------
+*This method is useful for those looking to run bleeding-edge versions of iceman's client. Keep this in mind when attempting to update your HomeBrew tap formula as this procedure could easily cause a build to break if an update is unstable on macOS.* 
+
+Tested on macOS Sierra 10.12.6
+
+*Note: This assumes you have already installed iceman's fork from HomeBrew as mentioned above*
+
+1. Force HomeBrew to pull the latest source from github
+`brew upgrade --fetch-HEAD iceman1001/proxmark3/proxmark3`
+
+2. Flash the bootloader
+  * With your Proxmark3 unplugged from your machine, press and hold the button on your Proxmark 3 as you plug it into a USB port. After about 5 seconds let go of the button and run this command
+   `$ sudo proxmark3-flasher /dev/tty.usbmodem881 /usr/local/Cellar/proxmark3/HEAD-ccfdd60/share/firmware/fullimage.elf`
+  * After the bootloader finishes flashing, unplug your Proxmark3 from your machine
+
+3. Flash fullimage.elf
+  * Press and hold the button on your Proxmark 3 and keep it held as you plug the Proxmark 3 back into the USB port; continue to hold the button until after this step is complete and the `proxmark3-flasher` command outputs "Have a nice day!"*
+
+`$ sudo proxmark3-flasher /dev/tty.usbmodem881 /usr/local/Cellar/proxmark3/HEAD-ccfdd60/share/firmware/fullimage.elf`
+
+4. Enjoy the update
 
 Compilling from source manually (Legacy)
 ---------------------------