Replace deprecated GitProcess usage in README with updated exec() API- (PR-#619)

[princeaden1]

I have created a PR on this issue: #619

Describe Issue The current README still references the deprecated GitProcess API, which may cause confusion for developers following the examples. Since Dugite now recommends using the new exec() API for Git operations, the documentation should be updated to match the current usage patterns.

I have a PR that replaces the deprecated examples with ones based on exec(), ensuring the documentation aligns with the latest API and best practices.