Update README.md to add alternatives for Norminette installation (#487)

* Add installation alternatives

I added installation alternatives due to possible PEP 668 error

* Add python3-setuptools installation

README.md

@@ -12,6 +12,25 @@ python3 -m pip install --upgrade pip setuptools
 python3 -m pip install norminette
 ```
 
+Install using pipx.
+```shell
+sudo apt update
+sudo apt install python3-setuptools
+sudo apt install pipx
+pipx install norminette
+pipx ensurepath
+```
+
+Install using a virtual environment.
+```shell
+python3 -m venv $HOME/.venv
+source $HOME/.venv/bin/activate
+python3 -m pip install --upgrade pip setuptools
+python3 -m pip install norminette
+echo "export PATH=\$PATH:$HOME/.venv/bin" >> $HOME/.${SHELL##/bin/}rc
+deactivate
+```
+
 To upgrade an existing install, use
 ```shell
 python3 -m pip install --upgrade norminette