Previously the phase was documented as `package` by default with
instructions to change it to `prepare-package` if you want to
include the documentation in the project's package. This led to some
confusion and sometimes the step to change it to `prepare-package`
was missed.
This commit updates the documentation to recommend that
`prepare-package` is always used. It works equally well for both
cases (packaging the documentation or not) and avoids the possible
confusion described above.
Closes gh-218
547c4f3fb1