doc: improve docs for main module

src/opentelemetry.ml

@@ -1,4 +1,8 @@
 
+(** Opentelemetry types and instrumentation *)
+
+(** {2 Wire format} *)
+
 (** Protobuf types *)
 module Proto = struct
   module Common = struct
@@ -44,6 +48,8 @@ module Proto = struct
   end
 end
 
+(** {2 Timestamps} *)
+
 (** Unix timestamp.
 
     These timestamps measure time since the Unix epoch (jan 1, 1970) UTC
@@ -61,6 +67,8 @@ module Timestamp_ns = struct
     Int64.(add d ns)
 end
 
+(** {2 Interface to data collector} *)
+
 (** Collector types
 
     These types are used by backend implementations, to send events to
@@ -170,6 +178,8 @@ module Util_ = struct
     res
 end
 
+(** {2 Identifiers} *)
+
 (** Trace ID.
 
     This 16 bytes identifier is shared by all spans in one trace. *)
@@ -208,6 +218,8 @@ end = struct
   let of_hex s = of_bytes (Util_.bytes_of_hex s)
 end
 
+(** {2 Attributes and conventions} *)
+
 module Conventions = struct
   module Attributes = struct
     module Process = struct
@@ -263,6 +275,8 @@ let _conv_key_value (k,v) =
 
 (**/**)
 
+(** {2 Global settings} *)
+
 (** Process-wide metadata, environment variables, etc. *)
 module Globals = struct
   open Proto.Common
@@ -309,6 +323,8 @@ module Globals = struct
     l |> merge_global_attributes_
 end
 
+(** {2 Traces and Spans} *)
+
 (** Events.
 
     Events occur at a given time and can carry attributes. They always
@@ -546,6 +562,8 @@ module Trace = struct
       raise e
 end
 
+(** {2 Metrics} *)
+
 (** Metrics.
 
     See {{: https://opentelemetry.io/docs/reference/specification/overview/#metric-signal} the spec} *)
@@ -628,6 +646,10 @@ module Metrics = struct
     Collector.send_metrics [rm] ~ret:ignore
 end
 
+module Logs = struct
+
+end
+
 (** {2 Utils} *)
 
 (** Implementation of the W3C Trace Context spec