docs: Add README for bme280 driver.

[nedseb]

Description

The bme280 driver is missing a README.

What to do

Create lib/bme280/README.md following the existing pattern (see lib/ism330dl/README.md for the most complete example):

1. Title — driver name and one-line description
2. Features — list of capabilities
3. I2C Address — check const.py for the default
4. Basic Usage — code snippet with import, init, and a simple read
5. API — list all public methods with short descriptions
6. Examples — table linking to examples/*.py files if they exist

Reference

• Model to follow: lib/ism330dl/README.md
• Driver code: lib/bme280/

Checklist

• README created at lib/bme280/README.md
• Covers all public methods

Note: This issue is blocked until the driver code is implemented. The lib/bme280/ directory is currently empty.

[nedseb]

Done in PR #314: lib/bme280/README.md created with full API documentation, sensor overview, usage examples, configuration reference, and a feature comparison table with other MicroPython BME280 drivers.