fix(dialog): Android manifest documentation

[otamam818]

As discussed in this draft pull request, added a section to this documentation that shows users how to add Android integration for external files in the dialog plug-in.

Feel free to change the explanation to suit the project

[otamam818]

UPDATE: I started working on including Android permissions within the Kotlin code of plugins-workspace/dialog and I imo this PR should be kept on hold from merging until that part is done (else it might be misleading to future users). Once I make a PR to include runtime permissions, I'll come back to this PR and update it accordingly

[amrbashir]

@otamam818 thank you for your work, let me know when you want me to review