Add usage doc comment for AnyValue type

opentelemetry/src/logs/record.rs

@@ -61,6 +61,14 @@ pub trait LogRecord {
 }
 
 /// Value types for representing arbitrary values in a log record.
+/// Note: The `tracing` and `log` crates only support basic types that can be
+/// converted to these core variants: `i64`, `f64`, `StringValue`, and `bool`.
+/// Any complex and custom types are supported through their Debug implementation,
+/// and converted to String. More complex types (`Bytes`, `ListAny`, and `Map`) are
+/// included here to meet specification requirements and are available to support
+/// custom appenders that may be implemented for other logging crates.
+/// These types allow for handling dynamic data structures, so keep in mind the
+/// potential performance overhead of using boxed vectors and maps in appenders.
 #[derive(Debug, Clone, PartialEq)]
 #[non_exhaustive]
 pub enum AnyValue {