docs: Add protobuf as a dev dependency

README.md

@@ -20,6 +20,10 @@ the stanza format of your preferred XMPP library yourself.
 
 ## Contributing
 
+Due to issues with `protobuf`, `omemo_dart` reimplements the Protobuf encoding for the required
+OMEMO messages. As such, `protobuf` is only a dependency for testing that the serialisation and
+deserialisation of the custom implementation.
+
 When submitting a PR, please run the linter using `dart analyze` and make sure that all
 tests still pass using `dart test`.
 

pubspec.yaml

@@ -9,12 +9,11 @@ dependencies:
   collection: ^1.16.0
   cryptography: ^2.0.5
   pinenacl: ^0.5.1
-  protobuf: ^2.1.0
   synchronized: ^3.0.0+2
 
 dev_dependencies:
   lints: ^2.0.0
+  protobuf: ^2.1.0
   protoc_plugin: ^20.0.1
   test: ^1.21.0
   very_good_analysis: ^3.0.1
-