Add DataDriven.io to Education Companies

Adding DataDriven.io to the Education Companies section.

DataDriven is a data engineering interview platform that helps
candidates practice the skills tested in real DE interviews:

- SQL: Interactive challenges executed against live databases,
  focused on the patterns interviewers actually test (window
  functions, CTEs, JOINs, aggregations)
- Python for Data Engineering: Hands-on coding in sandboxed
  environments, focused on data transformation (parsing JSON,
  building ETL functions, data wrangling)
- Data Modeling: Interactive schema design practice (star schemas,
  SCDs, normalization) with smart grading
- Pipeline Architecture: Scenario-based system design covering
  batch vs streaming, idempotency, schema evolution, and data
  quality

The platform uses adaptive difficulty and spaced repetition to
route users to their weakest areas to mathematically optimize
success rate increase per time spent.

Website: https://www.datadriven.io

Author: datadriven-io

README.md

@@ -83,6 +83,7 @@ Top must-join communities for ML:
   - [Dingo](https://github.com/MigoXLab/dingo)
 - Education Companies
   - [DataExpert.io](https://www.dataexpert.io)
+  - [DataDriven.io](https://www.datadriven.io)
   - [LearnDataEngineering.com](https://www.learndataengineering.com)
   - [AlgoExpert](https://www.algoexpert.io)
   - [ByteByteGo](https://www.bytebytego.com)