Added NOTICE.txt

- added both the `NOTICE.txt` and `LICENSE.txt` to the distribution

Original commit: elastic/x-pack-elasticsearch@5acfd50874

NOTICE.txt

@@ -0,0 +1,52 @@
+Elasticsearch Shield
+Copyright 2009-2015 Elastic
+
+---
+This product includes software developed by The Apache Software
+Foundation (http://www.apache.org/).
+
+
+---
+This product contains software distributed under
+Common Development and Distribution License 1.0 (CDDL)
+
+JavaMail API 1.5.3
+https://java.net/projects/javamail/pages/Home
+https://java.net/projects/javamail/pages/License
+
+JavaBeans Activation Framework 1.1.1
+http://www.oracle.com/technetwork/articles/java/index-135046.html
+
+---
+
+This product contains software developed by Mike Samuel. The
+following is the copyright and notice text for this software:
+
+    Copyright (c) 2011, Mike Samuel
+    All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+
+    Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+    Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in the
+    documentation and/or other materials provided with the distribution.
+    Neither the name of the OWASP nor the names of its contributors may
+    be used to endorse or promote products derived from this software
+    without specific prior written permission.
+    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+    COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+    POSSIBILITY OF SUCH DAMAGE.
+

src/main/assemblies/plugin.xml

@@ -31,4 +31,14 @@
             </includes>
         </dependencySet>
     </dependencySets>
+    <files>
+        <file>
+            <source>LICENSE.txt</source>
+            <outputDirectory>/</outputDirectory>
+        </file>
+        <file>
+            <source>NOTICE.txt</source>
+            <outputDirectory>/</outputDirectory>
+        </file>
+    </files>
 </assembly>