Create Mac-OS-X-Compile-From-Source-Instructions.md

New documentation file to provide installation from source instructions on MacOS. This procedure has been tested on MacOS Big Sur.

doc/md/Installation_Instructions/Mac-OS-X-Compile-From-Source-Instructions.md

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+# Mac OS X - Compilation from source instructions
+
+# Table of Contents
+- [Mac OS X - Compilation from source instructions](x#mac-os-x---compilation-from-source-instructions)
+- [Table of Contents](#table-of-contents)
+  - [Installing build prerequisites via Homebrew](#installing-build-prerequisites-via-homebrew)
+  - [Configure the build](#configure-the-build)
+  - [Compilation from source](#compilation-from-source)
+
+## Installing build prerequisites via Homebrew
+^[Top](#top)
+
+We need to install the ``openssl`` library with ``brew``:
+```bash
+brew install openssl
+```
+To run the local install script below, we also require the GNU versions 
+of several core Unix utilities:
+```bash
+brew install coreutils
+```
+
+## Configure the build
+^[Top](#top)
+
+Clone the repository by running the following:
+```bash
+git clone https://github.com/RfidResearchGroup/proxmark3.git
+cd proxmark3
+```
+Configure the build by editing ``Makefile.platform``:
+```bash
+cp Makefile.platform.sample Makefile.platform
+vim Makefile.platform
+```
+
+## Compilation from source
+^[Top](#top)
+
+The following command has been shown to work on MacOS Big Sur with the 
+default Compiler Tools that comes installed on this release of the platform:
+```bash
+make clean && CFLAGS="" make
+```
+If you have ``sudo`` rights, you can install the proxmark3 utilities into the system 
+path by running
+```bash
+sudo make install
+```
+Otherwise, assuming you are using the ``bash`` shell (using ``chsh -s /bin/bash `whoami```), we can create 
+an alias to the relevant commands:
+```bash
+export BASHRC="~/.bash_profile"
+export PM3LOCAL_PATH="$(greadlink -f .)"
+touch $BASHRC
+echo "alias pm3=\'$PM3LOCAL_PATH/pm3\'" >> $BASHRC
+echo "alias pm3-flash=\'$PM3LOCAL_PATH/pm3-flash\'" >> $BASHRC
+echo "alias pm3-flash-all=\'$PM3LOCAL_PATH/pm3-flash-all\'" >> $BASHRC
+echo "alias pm3-flash-bootrom=\'$PM3LOCAL_PATH/pm3-flash-bootrom\'" >> $BASHRC
+echo "alias pm3-flash-fullimage=\'$PM3LOCAL_PATH/pm3-flash-fullimage\'" >> $BASHRC
+```
+When you are done running the previous script, make sure to update the settings in your 
+current shell (Mac Terminal) instance by running
+```bash
+source ~/.bash_profile
+```
+When you re-start the Mac terminal, new shell instances will automatically load these 
+new settings.