feat(docs): add tracing example

[joshka]

Add an example that demonstrates logging to a file for: https://forum.ratatui.rs/t/how-do-you-println-debug-your-tui-programs/66

cargo run --example tracing
RUST_LOG=trace cargo run --example=tracing
cat tracing.log

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.4%. Comparing base (127d706) to head (e4c432a). Report is 1 commits behind head on main.

:exclamation: Current head e4c432a differs from pull request most recent head 8ec4aaa

Please upload reports for the commit 8ec4aaa to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1192 +/- ## ======================================= - Coverage 94.4% 94.4% -0.1% ======================================= Files 62 62 Lines 14935 14941 +6 ======================================= + Hits 14105 14110 +5 - Misses 830 831 +1 ```

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[EdJoPaTo]

Should probably wait for #1180 or #1189? Otherwise, it will result in more merge conflicts.

[joshka]

Should probably wait for #1180 or #1189? Otherwise, it will result in more merge conflicts.

I'm fine with fixing up merge conflicts later. I'd prefer that over leaving a large amount of things which are good enough in a pending state.