Added a PHONY target to avoid a conflict with a file of the same name, and to improve performance.

Also made minor changes to the README

Information was found here: [GNU make](https://www.gnu.org/software/make/manual/make.html#Phony-Targets)

## tl;dr

> A phony target is one that is not really the name of a file; rather it is just a name for a recipe to be executed when you
> make an explicit request. There are two reasons to use a phony target: to avoid a conflict with a file of the same name,
> and to improve performance.

> make skips the implicit rule search for phony targets (see Implicit Rules). This is why declaring a target phony is good 
> for performance, even if you are not worried about the actual file existing.