Better installation instructions

The current installation instructions are not sufficient for making ttx work. To illustrate the issue:

$ pip install fonttools
Requirement already satisfied: fonttools in /Library/Python/2.7/site-packages (3.32.0)
$ ttx
-bash: ttx: command not found

Or:

$ pip install -e .
Obtaining file://~/Repositories/GitHub/fonttools
    Complete output from command python setup.py egg_info:
    error in fonttools setup command: 'extras_require' must be a dictionary whose values are strings or lists of strings containing valid project/version requirement specifiers.
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in ~/Repositories/GitHub/fonttools/

[anthrotype]

Also note when installing with --user the executable scripts are not placed under /usr/local/bin, but under the user’s bin directory (in my case /Users/clupo/Library/Python/3.7/bin). This is not already in the $PATH, so you will have to append to it in your shell config file (e.g. .bashrc). So --user adds a further layer of complexity. Whereas /usr/local/bin/ is already in the default executable $PATH.

[BoldMonday]

Is Homebrew still necessary to install Python 3? I used it in the past but found it hard to upgrade to newer Python versions.

On my current Mojave machine I installed Python 3.8.2 with the official installer from Python.org. Seems to work fine.