Update Chapter 20: Access to Data

[claudio-rosati]

Hello all,

I think Chapter 20. Access to Data should be updated, specially after the integration of the new DIIRT library by @shroffk and @kasemir.

I'll add a new paragraph related to the initialization of the diirt.home preference inside plugin_customization.ini where @user.home or platform: syntax can be used. Or do you think it is better to add it in Chapter 6. Hierarchical Preferences?

[kasemir]

Yes, when we're done, we need to update the access to data chapter.

When you're done with the preference changes, I agree that they should be mentioned in the Hierarchical Preferences chapter.