Add documentation for @Traced

Author: porglezomp

Sources/TracingMacros/TracedMacro.swift

@@ -15,11 +15,26 @@
 import Tracing
 
 #if compiler(>=6.0)
+/// Instrument a function to place the entire body inside a span.
+///
+/// This macro is equivalent to calling ``/Tracing/withSpan`` in the body, but saves an
+/// indentation level and duplication. It introduces a `span` variable into the
+/// body of the function which can be used to add attributes to the span.
+///
+/// Parameters are passed directly to ``/Tracing/withSpan`` where applicable,
+/// and omitting the parameters from the macro omit them from the call, falling
+/// back to the default.
+///
+/// - Parameters:
+///   - operationName: The name of the operation being traced. Defaults to the name of the function.
+///   - context: The `ServiceContext` providing information on where to start the new ``/Tracing/Span``.
+///   - kind: The ``/Tracing/SpanKind`` of the new ``/Tracing/Span``.
+///   - spanName: The name of the span variable to introduce in the function. Pass `"_"` to omit it.
 @attached(body)
 public macro Traced(
     _ operationName: String? = nil,
     context: ServiceContext? = nil,
     ofKind kind: SpanKind? = nil,
-    span spanName: String? = nil
+    span spanName: String = "span"
 ) = #externalMacro(module: "TracingMacrosImplementation", type: "TracedMacro")
 #endif