Add SCons install instructions to new website

[ischoegl]

Changes proposed in this pull request

Add installation instructions to new documentation and fix some minor glitches.

Checklist

• [x] The pull request includes a clear description of this code change
• [x] Commit messages have short titles and reference relevant issues
• [x] Build passes (scons build & scons test) and unit tests address code coverage
• [x] Style & formatting of contributed code follows contributing guidelines
• [x] The pull request is ready for review

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.12%. Comparing base (3196d5e) to head (ef197f0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1766 +/- ## ======================================= Coverage 73.12% 73.12% ======================================= Files 381 381 Lines 54174 54174 Branches 9223 9223 ======================================= Hits 39615 39615 Misses 11598 11598 Partials 2961 2961 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.