Update documentation regarding LegendHDF5IO

[fhagemann]

Recently, loading LegendHDF5IO before SolidStateDetectors would result in

┌ Warning: Error requiring `LegendHDF5IO` from `SolidStateDetectors`
│   exception =
│    LoadError: ConcurrencyViolationError("deadlock detected in loading SolidStateDetectors -> SolidStateDetectors")

However, all of this is fine if SolidStateDetectors is loaded before LegendHDF5IO.

In the documentation, we previously required all HDF5-related packages to be loaded before SolidStateDetectors. I updated the documentation such that we recommend loading them afterwards. Also, the package HDF5 is no longer explicitly required.