add documentation of RA_LOG_FILE
@@ -132,6 +132,7 @@ Logging is done by both rust-analyzer and VS Code, so it might be tricky to figu
Inside rust-analyzer, we use the standard `log` crate for logging, and `env_logger` for logging frontend.
By default, log goes to stderr, but the stderr itself is processed by VS Code.
`--log-file <PATH>` CLI argument allows logging to file.
+Setting the `RA_LOG_FILE=<PATH>` environment variable will also log to file, it will also override `--log-file`.
To see stderr in the running VS Code instance, go to the "Output" tab of the panel and select `rust-analyzer`.
This shows `eprintln!` as well.
