Update developer documentation

[lyashevska]

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Testing local changes to the template

pipx install copier

To test your local modifications, you can run copier with the --vcs-ref HEAD flag and point to your local clone. This will use the latest changes, including uncommitted modifications (i.e., the dirty state).

cd $(mktemp -d) # Go to a tmp folder
copier copy --vcs-ref HEAD /path/to/clone/ pkg # Clone dirty clone into pkg