Add Apache-2.0 license and some note to README.md. (#9)

* Add Apache-2.0 license and some notes to README.md.
* Add user link.
* update.

NOTICE

@@ -0,0 +1,26 @@
+###################################################################################
+
+The following modifications follow Apache License 2.0 from shiguredo.
+
+https://github.com/webrtc-sdk/webrtc/commit/dfec53e93a0a1cb93f444caf50f844ec0068c7b7
+https://github.com/webrtc-sdk/webrtc/commit/403b4678543c5d4ac77bd1ea5753c02637b3bb89
+https://github.com/webrtc-sdk/webrtc/commit/77d5d685a90fb4bded17835ae72ec6671b26d696
+
+Apache License 2.0
+
+Copyright 2019-2021, Wandbox LLC (Original Author)
+Copyright 2019-2021, Shiguredo Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+#####################################################################################

README.md

@@ -1,3 +1,23 @@
+# WebRTC-SDK
+
+This is a **Community-Maintained** project, **Not the official Google WebRTC repository**. It is maintained by some contributors with WebRTC development experience, and the goal is to create a flexible release version to provide pre-compiled Mobile/Desktop/Embedded SDKs.
+
+## Additional notes from [webrtc-sdk](https://github.com/webrtc-sdk) community
+
+### Open Source License Compliance
+
+* The original code was cloned from [google webrtc](https://chromium.googlesource.com/external/webrtc.git) and released with [BSD license](/LICENSE).
+
+* Contains patches from the [shiguredo-webrtc-build](https://github.com/shiguredo-webrtc-build) community and complies with the [Apache 2.0](/NOTICE) license.
+
+### Who is using this project
+
+* [flutter-webrtc](https://github.com/flutter-webrtc/flutter-webrtc)
+
+* [LiveKit](https://github.com/livekit)
+
+## The Google WebRTC original README
+
 **WebRTC is a free, open software project** that provides browsers and mobile
 applications with Real-Time Communications (RTC) capabilities via simple APIs.
 The WebRTC components have been optimized to best serve this purpose.