Add a help target to Makefile

## Utilize GNU Make documentation to create a help target

### Requirements
- Update make file with a command that lists what commands can be done
- e.g. use @echo to list the targets and what they do
- List all the commands/target within main
- Default make, clean, and help

Resources to see examples of targets and Make documentation can be found [here](https://www.gnu.org/software/make/manual/html_node/Rules.html#Rules).

Make sure to test within your terminal to see that the code compiles and works correctly!