Add package-level document for api and adapter/micro package

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

adapter/micro/doc.go

@@ -0,0 +1,21 @@
+/*
+This package provides Sentinel integration for go-micro.
+
+For server side, users may append a Sentinel handler wrapper to go-micro service, like:
+
+		import (
+			sentinelPlugin "github.com/alibaba/sentinel-golang/adapter/micro"
+		)
+
+		// Append a Sentinel handler wrapper.
+		micro.NewService(micro.WrapHandler(sentinelPlugin.NewHandlerWrapper()))
+
+The plugin extracts service method as the resource name by default.
+Users may provide customized resource name extractor when creating new
+Sentinel handler wrapper (via options).
+
+Fallback logic: the plugin will return the BlockError by default
+if current request is blocked by Sentinel rules. Users may also
+provide customized fallback logic via WithXxxBlockFallback(handler) options.
+*/
+package micro

api/api.go

@@ -1,3 +1,4 @@
+// Package api provides fundamental APIs of Sentinel.
 package api
 
 import (