Don't generate pipx install instructions for libraries

[seanh]

These instructions make sense for command line packages but not for libraries or tox plugins:

cookiecutters/pypackage/{{ cookiecutter.slug }}/INSTALL.md

Lines 1 to 39 in cc07942

	# Installing {{ cookiecutter.name }}
	We recommend using [pipx](https://pypa.github.io/pipx/) to install
	{{ cookiecutter.name }}.
	First [install pipx](https://pypa.github.io/pipx/#install-pipx) then run:
	```terminal
	pipx install {{ cookiecutter.slug }}
	```
	You now have {{ cookiecutter.name }} installed! For some help run:
	```
	{{ cookiecutter.__entry_point }} --help
	```
	Upgrading
	---------
	To upgrade to the latest version run:
	```terminal
	pipx upgrade {{ cookiecutter.slug }}
	```
	To see what version you have run:
	```terminal
	{{ cookiecutter.__entry_point }} --version
	```
	Uninstalling
	------------
	To uninstall run:
	```
	pipx uninstall {{ cookiecutter.slug }}
	```