update documentation with instructions to provide public access to …

[IBM-Deeksha]

Added steps to provide public access to a bucket via terraform.

Contributes to: https://github.com/IBM-Cloud/terraform-provider-ibm/issues/1268

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Relates OR Closes #0000

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccXXX'

...

[IBM-diksha]

Looks good to me!