copy pasta in ARCHITECTURE.md

[drew-moore]

https://github.com/src-d/proteus/blob/master/ARCHITECTURE.md#protobuf-transformer:

Even though the step is transforming, it's inside the protobuf package to note that it's transforming the scanner.Package into a protobuf package.

Either you meant to say "it's important to note that...", or this is way too meta for me :)