Define OTLP 1.0 Stability guarantees

Resolves open-telemetry#400

README.md

@@ -43,32 +43,34 @@ for definition of maturity levels).
 
 Components marked `Stable` provide the following guarantees:
 
-- Field types will not change.
-- Field numbers will not change.
-- Numbers assigned to enum choices will not change.
-- Service names and service package names will not change.
-- Service operation names, parameter and return types will not change.
+- Field types, numbers and names will not change.
+- Names of messages and enums will not change.
+- Names of enum choices and numbers assigned to enum choices will not change.
+- The location of messages and enums, i.e. whether they are declared at the top lexical
+  scope or nested inside another message will not change.
+- Package names and directory structure will not change.
+- gRPC service names, service method names, parameters and return types will not change.
+- Service method parameter names will not change.
+- Service method kind (unary vs streaming) will not change.
+- No existing symbol will be deleted.
+- `optional` and `repeated` declarators of existing fields will not change.
 
 The following changes are allowed:
 
-- Message names may change.
-- Field names may change.
-- Enum names may change.
-- Enum choice names may change.
-- The location of messages and enums, i.e. whether they are declared at the top
-  lexical scope or nested inside another message may change.
-- Package names may change.
-- Directory structure, location and the name of the files may change.
+- Adding new fields to existing messages.
+- Adding new messages or enums.
+- Adding new choices to existing enums.
+- Adding new choices to existing oneof fields.
+- Adding new services.
+- Adding new methods to existing services. 
 
-Note that none of the above allowed changes affects the binary wire representation.
+All the allowed changes above must be accompanied by an explanation about how
+new and old senders and receivers that implement the version of the protocol
+before and after the change interoperate.
 
-No guarantees are provided whatsoever about the stability of the code that
+WARNING: No guarantees are provided whatsoever about the stability of the code that
 is generated from the .proto files by any particular code generator.
 
-In the future when OTLP/JSON is declared stable, several of the changes that
-are currently allowed will become disallowed since they are visible on the wire
-for JSON encoding.
-
 ## Experiments
 
 In some cases we are trying to experiment with different features. In this case,