Set up release makefile and doc. (#14)

Makefile

+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You 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.
+
+SHELL := /bin/bash -o pipefail
+
+VERSION ?= latest
+RELEASE_SRC = skywalking-nginx-lua-${VERSION}-src
+
+release-src:
+	tar -zcvf $(RELEASE_SRC).tgz \
+	--exclude bin \
+	--exclude .git \
+	--exclude .idea \
+	--exclude .gitignore \
+	--exclude .DS_Store \
+	--exclude .github \
+	.
+
+	gpg --batch --yes --armor --detach-sig $(RELEASE_SRC).tgz
+	shasum -a 512 $(RELEASE_SRC).tgz > $(RELEASE_SRC).tgz.sha512
+
+	mkdir -p release
+	mv $(RELEASE_SRC).tgz release/$(RELEASE_SRC).tgz
+	mv $(RELEASE_SRC).tgz.asc release/$(RELEASE_SRC).tgz.asc
+	mv $(RELEASE_SRC).tgz.sha512 release/$(RELEASE_SRC).tgz.sha512
\ No newline at end of file

README.md

@@ -68,6 +68,14 @@ http {
 }
 ```
 
+# Download
+Please head to the [releases page](http://skywalking.apache.org/downloads/) to download a release of Apache SkyWalking.
+
+# Compatible backend
+SkyWalking OAP begins to support LUA agent in 7.0.0 release. 
+
+You could choose master branch before the official 7.0.0 release.
+
 # Set up dev env
 ### Debug Startup
 By using the `/examples/nginx.conf`, you could start the Nginx with LUA module or OpenResty. Such as `nginx -c /path/to/skywalking-nginx-lua/examples/nginx.conf`
@@ -121,14 +129,17 @@ Create 2 kinds of span
 - `TracingContext.createExitSpan(operationName, parent, peer, contextCarrier)`
 
 
-# Download
-Have no release yet.
-
 # Contact Us
 * Submit an [issue](https://github.com/apache/skywalking/issues) with `[NIGNX-LUA]` as the issue title prefix.
 * Mail list: **dev@skywalking.apache.org**. Mail to `dev-subscribe@skywalking.apache.org`, follow the reply to subscribe the mail list.
 * Join `skywalking` channel at [Apache Slack](https://join.slack.com/t/the-asf/shared_invite/enQtNzc2ODE3MjI1MDk1LTAyZGJmNTg1NWZhNmVmOWZjMjA2MGUyOGY4MjE5ZGUwOTQxY2Q3MDBmNTM5YTllNGU4M2QyMzQ4M2U4ZjQ5YmY). If the link is not working, find the latest one at [Apache INFRA WIKI](https://cwiki.apache.org/confluence/display/INFRA/Slack+Guest+Invites).
 * QQ Group: 392443393(2000/2000, not available), 901167865(available)
 
+# Release Tar Build
+```shell
+> export VERSION=x.y.z
+> make release-src
+```
+
 # License
 Apache 2.0