Clarify installation steps (conda environments)

[raquo]

This PR is clarifying that the installation instructions are talking about conda environments and not python environments. I'm new to all this so not 100% sure that this is the right thing to say, but it seemed to work for me.

[jmwright]

@raquo Thanks for doing this. Could you please merge master into your branch? That should fix the failing checks.

[codecov]

Codecov Report

Merging #908 (9ea6dab) into master (d6c41d7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #908   +/-   ##
=======================================
  Coverage   96.11%   96.11%           
=======================================
  Files          39       39           
  Lines        9130     9130           
  Branches     1017     1017           
=======================================
  Hits         8775     8775           
  Misses        206      206           
  Partials      149      149           

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[raquo]

@jmwright So I've just rebased my branch on CadQuery/cadquery master, which is at d6c41d7 as I type this. Now my branch has d6c41d7 as the second-to-last commit, and the last commit is my actual docs change. Still, some checks are failing, not sure why.

[adam-urbanczyk]

Small doc change - merging. Thanks @raquo !