Update README.md

[Trojan-254]

In this update, i have expanded the README.md documentation for the env_logger crate to provide a more comprehensive and user-friendly guide. The following changes and enhancements have been made:

Enhanced Introduction: I have clarified the purpose and appropriate use cases for env_logger, emphasizing its utility in executable projects and recommending the use of the log crate for libraries.

Detailed Usage Instructions:

Dependency Setup: Expanded instructions on adding both log and env_logger crates to your project dependencies using cargo add.
Initialization: Provided guidance on initializing env_logger as early as possible in your project, with clear examples demonstrating the logging process.
Environment Variable Configuration: Included detailed explanations on how to configure logging levels using the RUST_LOG environment variable, with examples showcasing different level configurations.
Logging Levels Explained:

A comprehensive table has been added to explain the different logging levels (error, warn, info, debug, trace), along with their appropriate use cases.

These additions aim to make the documentation more informative and accessible, helping users get the most out of the env_logger crate, whether they are new to Rust logging or experienced developers looking to optimize their application's logging setup.

[Trojan-254]

Please review

[epage]

A lot of the existing README is duplicating https://docs.rs/env_logger/latest/env_logger/ and this is expanding it further. I would be inclined to consider what improvements should be made to https://docs.rs/env_logger/latest/env_logger/ and instead have the README show a simple example, pointing people to https://docs.rs/env_logger/latest/env_logger/ for more details.