BUG: Restore commented extras_require in install.rst

[rstoneback]

Description

RTD and the documentation checks are currently unhappy with the extras_require in install.rst . Currently commented out. Restore once RTD and such sorts themselves out.

To Reproduce this bug:

Steps to reproduce the behavior:

1. Run unit tests with extras_require in install.rst
2. RTD will produce an error

Error:
Exception occurred:
File "/opt/hostedtoolcache/Python/3.10.15/x64/lib/python3.10/site-packages/tomli/_parser.py", line 716, in parse_value
return parse_inline_table(src, pos, parse_float, nest_lvl + 1)
TypeError: TomlDecoder.loads.._parse_inline_table() takes 3 positional arguments but 4 were given

Test configuration

• online unit tests

Additional context

Add any other context about the problem here, including expected behaviour.