Update README.md: typos in comment and fixing error in the command

[systemlogic]

Updating documentation for cuxfilter-cu-1x and adding extra dash - so that command will work just fine.

The intention of the Pull request is to fix the typo and command so that Engineers can simply copy the command from reference codument and make it work on their desire environment.

[copy-pr-bot[bot]]

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[systemlogic]

Testing Done:

/content# pip install cuxfilter-cu12 -extra-index-url=https://pypi.nvidia.com
ERROR: xtra-index-url=https://pypi.nvidia.com is not a valid editable requirement. It should either be a path to a local project or a VCS URL (beginning with bzr+http, bzr+https, bzr+ssh, bzr+sftp, bzr+ftp, bzr+lp, bzr+file, git+http, git+https, git+ssh, git+git, git+file, hg+file, hg+http, hg+https, hg+ssh, hg+static-http, svn+ssh, svn+http, svn+https, svn+svn, svn+file).
/content# echo $?
1

post changes

pip install cuxfilter-cu12 --extra-index-url=https://pypi.nvidia.com
Requirement already satisfied: types-python-dateutil>=2.8.10 in /usr/local/lib/python3.12/dist-packages (from arrow>=0.15.0->isoduration->jsonschema[format-nongpl]>=4.18.0->jupyter-events>=0.9.0->jupyter-server>=1.24.0->jupyter-server-proxy->cuxfilter-cu12) (2.9.0.20250822)
/content# echo $?
0