docs: fix did doc config example in did lib README.md

Description

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Fixes #765

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] This change requires a documentation update

[ ] I have performed a self-review of my code
[ ] If it is a core feature, I have added thorough tests
[ ] Do we need to implement analytics?
[ ] Will this be part of a product update? If yes, please write one phrase about this update.
[ ] My code follows the style guidelines of this project
[ ] I have commented my code, particularly in hard-to-understand areas
[ ] I have made corresponding changes to the documentation
[ ] My changes generate no new warnings
[ ] I have added tests that prove my fix is effective or that my feature works
[ ] New and existing unit tests pass locally with my changes
[ ] Any dependent changes have been merged and published in downstream modules