Add readme about how to provide configuration to the collector (#5507)
Add readme about how to provide configuration to the collector (#5507)

This explains only how to provide the configuration via the `--config` file, after #4742 will update the embedded values option.

Signed-off-by: Bogdan Drutu <3f8e17047c2434e5c82a61403e56b9ef3e226d99@gmail.com>
open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector