Recommend pipx for a simple install process

[yolabingo]

1. Please specify the following:

• OS: OS X, linux, windows

• Shell: Most any

• [x ] I have reviewed the troubleshooting tips described here and they do not solve my problem

2. Description
Add pipx as an install method in the README.

Install instructions:

1. Install pipx
2. pipx install awsebcli

Using pipx is much simpler than manually managing python vitualenvs. Pipx is an established, stable, tool that drastically improves the installation process of many, python-based, cli apps.
Pipx all but eliminates the concerns mentioned here: whats-the-advantage-of-this-mode-of-installation-instead-of-regular-pip-inside-a-virtualenv

[dustinbolton]

@yolabingo Thank you for sharing this. I spent hours trying to get things to work using pip and virtualenv. The install instructions failed repeatedly on my new Mac. pipx got everything working for me instantly.

[bradwbradw]

I installed using pipx, and then when I tried out eb i got:

 $ eb create my-env       
Traceback (most recent call last):
  File "/Users/brad/.local/bin/eb", line 7, in <module>
    from ebcli.core.ebcore import main
  File "/Users/brad/Library/Application Support/pipx/venvs/awsebcli/lib/python3.12/site-packages/ebcli/core/ebcore.py", line 16, in <module>
    from cement.core import foundation, handler, hook
  File "/Users/brad/Library/Application Support/pipx/venvs/awsebcli/lib/python3.12/site-packages/cement/core/foundation.py", line 11, in <module>
    from ..core import output, extension, arg, controller, meta, cache, mail
  File "/Users/brad/Library/Application Support/pipx/venvs/awsebcli/lib/python3.12/site-packages/cement/core/extension.py", line 8, in <module>
    from imp import reload  # pragma: no cover
    ^^^^^^^^^^^^^^^^^^^^^^
ModuleNotFoundError: No module named 'imp'

(edit) i see now it is an eb issue after all: #153

[yolabingo]

@bradwbradw
you can tell pipx to use an older python version by specifying another python executable on your path, for example
pipx install --python python3.11 awsebcli