Add README, fix copyright issues

Signed-off-by: Vladimir Popov <vladimir.popov@xored.com>

pkg/tools/clientmap/README.md

@@ -0,0 +1,23 @@
+# clientmap.Map
+
+It is a `sync.Map` typed for the `string` keys and `networkservice.NetworkServiceClient` values.
+
+# clientmap.RefcountMap
+
+It is a `clientmap.Map` wrapped with refcounting:
+```
+Store, LoadOrStore (store)  -->  count = 1
+Load, LoadOrStore (load)    -->  count += 1
+LoadAndDelete, Delete       -->  count -= 1
+```
+if count becomes 0, value deletes.
+
+## Performance
+
+`clientmap.RefcountMap` is a very thin wrapper, it doesn't hardly affect the `clientmap.Map` performance:
+```
+BenchmarkMap
+BenchmarkMap-4           	15998454	        84.6 ns/op
+BenchmarkRefcountMap
+BenchmarkRefcountMap-4   	10496374	       106 ns/op
+```

pkg/tools/clientmap/refcount.go

@@ -1,5 +1,7 @@
 // Copyright (c) 2020 Doc.ai and/or its affiliates.
 //
+// Copyright (c) 2020 Cisco and/or its affiliates.
+//
 // SPDX-License-Identifier: Apache-2.0
 //
 // Licensed under the Apache License, Version 2.0 (the "License");

pkg/tools/clientmap/refcount_test.go

@@ -1,3 +1,5 @@
+// Copyright (c) 2020 Doc.ai and/or its affiliates.
+//
 // Copyright (c) 2020 Cisco and/or its affiliates.
 //
 // SPDX-License-Identifier: Apache-2.0