update Migration guide: info about the changed behavior

[ckeshava]

High Level Overview of Change

This PR includes additional information about the default signing algorithm in the migration guide. We hope this reduces the confusion amongst the library users.

Type of Change

• [ ] 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)
• [ ] Refactor (non-breaking change that only restructures code)
• [ ] Tests (You added tests for code that already exists, or your new feature included in this PR)
• [x] Documentation Updates
• [ ] Release

Did you update HISTORY.md?

• [ ] Yes
• [ ] No, this change does not impact library users This PR does not have any material code changes

[ckeshava]

thnks @JST5000 for helping me re-word the migration guide. let me know if this looks alright ^^

[ckeshava]

@mvadari do the changes look okay? I believe I have addressed your comments