Mutations are important, but we can explain relative and private mutations only in context of tree and clades, so it feels better to put "mutation calling" section after tree placement and clade assignment.

Following #1499, conda is unable to find required version of sphinx:

```
0.098 + /opt/conda/bin/conda env create -n docs.clades.nextstrain.org
0.501 Channels:
0.501  - defaults
0.501 Platform: linux-64
0.501 Collecting package metadata (repodata.json): ...working... done
2.229 Solving environment: ...working... failed
2.439 
2.439 PackagesNotFoundError: The following packages are not available from current channels:
2.439 
2.439   - sphinx=7.2*
2.439 
2.439 Current channels:
2.439 
2.439   - https://repo.anaconda.com/pkgs/main/linux-64
2.439   - https://repo.anaconda.com/pkgs/r/linux-64
2.439 
2.439 To search for alternate channels that may provide the conda package you're
2.439 looking for, navigate to
2.439 
2.439     https://anaconda.org
2.439 
2.439 and use the search bar at the top of the page.
```


Let's try and add coda-forge channel