add the sentiment service

sentiment/proto/sentiment.proto

@@ -0,0 +1,23 @@
+syntax = "proto3";
+
+package sentiment;
+
+option go_package = "./proto;sentiment";
+
+service Sentiment {
+	rpc Analyze(Request) returns (Response) {};
+}
+
+// Analyze and score a piece of text
+message Request {
+	// The text to analyze
+	string text = 1;
+	// The language. Defaults to english.
+	string lang = 2;
+}
+
+message Response {
+	// The score of the text
+	double score = 1;
+}
+