add simple php example

example-php-apache/Dockerfile

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+# SEE: https://hub.docker.com/_/php
+FROM php:7.2-apache
+LABEL maintainer="[email protected]"
+
+# expose port 80 for http://
+EXPOSE 80
+
+# expose port 443 for https://
+EXPOSE 443
+
+# copy all files from src directory
+COPY src/ /var/www/html/
+
+# allow changes to auto-populate when running local dev environment
+VOLUME src/ /var/www/html/

example-php-apache/README.md

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+# Docker - simple PHP server
+
+Follow these steps to start the php server:
+
+```
+cd /path/to/example-php-apache
+docker build -t example-php-apache-img .
+docker run -p 3000:80 -v $(pwd)/src:/var/www/html --name example-php-apache-container example-php-apache-img
+```
+
+Open up the following url in your browser:
+
+- http://localhost:3000
+
+
+# Notes
+
+In the `docker run` command:
+- `-p` maps ports like so: `<MACHINE_PORT>:<CONTAINER_PORT>`
+- `-v` specifies the volume to enable realtime updates in local dev environment.
+  - The volume must be specified at runtime in order for this to work. [See documentation](https://docs.docker.com/engine/reference/builder/#notes-about-specifying-volumes) for more details.
+  - The host volume mount src MUST be absolute, not relative
+  - `$(pwd)` just outputs the absolute path of the present working directory
+  - Volumes have ZERO effect once deployed (except for sharing filesystems across several containers)

example-php-apache/src/index.php

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+<?php
+echo "Hello world";