up to date protobuf building documentation

// FREEBIE

protobuf/Makefile

@@ -1,8 +1,7 @@
-# Assumes you've installed protobug-objc
-# see: https://github.com/alexeyxo/protobuf-objc
+# See README.md in this dir for prerequisite setup.
 
 PROTOC=protoc \
-		--plugin=/usr/local/bin/proto-gen-objc \
+		--plugin=/usr/local/bin/protoc-gen-objc \
 		--proto_path="${HOME}/src/WhisperSystems/protobuf-objc/src/compiler/" \
 		--proto_path="${HOME}/src/WhisperSystems/protobuf-objc/src/compiler/google/protobuf/" \
 		--proto_path='./'

protobuf/README.md

@@ -0,0 +1,38 @@
+# SignalServiceKit Protobufs
+
+These protobuf definitions are copied from Signal-Android, but modified
+to include a conventional ObjC classnames.
+
+e.g.
+
+    import "objectivec-descriptor.proto";
+    option (google.protobuf.objectivec_file_options).class_prefix = "OWSFingerprintProtos";
+
+## Prequisites
+
+Install protobuf 2.6, the objc plugin doesn't currently work with
+protobuf 3.0
+
+    brew install protobuf@2.6
+    # Beware if you are depending on protobuf 3.0 elsewhere
+    brew link --force protobuf@2.6
+
+Install the objc plugin to $SignalServiceKitRoot/..
+
+e.g. I have SignalServiceKit installed to ~/src/WhisperSystems/SignalServiceKit
+
+So I run
+
+    cd ~/src/WhisperSystems
+    git clone https://github.com/alexeyxo/protobuf-objc
+
+Follow the install instructions at https://github.com/alexeyxo/protobuf-objc
+
+## Building Protobuf
+
+After changes are made to any proto, generate the ObjC classes by
+running:
+
+    cd ~/src/WhisperSystems/SignalServiceKit/protobuf
+    make
+