docs: get all data using Promise

[theanishtar]

• Add code snippet to retrieve all keys from Redis using the wildcard '*'.
• When keys are available, fetch the corresponding values entirely.
• Handle asynchronous processing with promises.

[theanishtar]

Recognizing the missing section on fetching all data from Redis in the documents, I have added it to the README.md file. I hope the contribution will be acknowledged!!! Thank you for reading.