missing "Conda installation instructions" link

[JacekHoleczek]

The main User information web page contains an invalid link: [Conda installation instructions](Conda installation instructions)

[eduardo-rodrigues]

FYI @henryiii is trying to fix a few links in PR #349 following the move of a lot of material to the scientific-python developer pages. The link is being added back in there hence I will make that PR close this.

Thanks for the report and interest in our material :-).

[eduardo-rodrigues]

The link is presently valid, see https://scikit-hep.org/user/installing-conda/. I also fixed the other 2 links mentioned in the PR "fix: links #349" above (see b3e4523).