Fix copyright notice and add DCO check workflow (#94)

Signed-off-by: Ashish Agrawal <ashisagr@amazon.com>

.github/workflows/dco.yml

@@ -0,0 +1,18 @@
+name: Developer Certificate of Origin Check
+
+on: [pull_request]
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Get PR Commits
+        id: 'get-pr-commits'
+        uses: tim-actions/get-pr-commits@v1.1.0
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+      - name: DCO Check
+        uses: tim-actions/dco@v1.1.0
+        with:
+          commits: ${{ steps.get-pr-commits.outputs.commits }}

CONTRIBUTING.md

@@ -1,4 +1,51 @@
 ## Contributing to this Project
 
 OpenSearch is a community project that is built and maintained by people just like **you**. 
-[This document](https://github.com/opensearch-project/.github/blob/main/CONTRIBUTING.md) explains how you can contribute to this and related projects.
+[This document](https://github.com/opensearch-project/.github/blob/main/CONTRIBUTING.md) explains how you can contribute to this and related projects.
+
+## Developer Certificate of Origin
+
+OpenSearch is an open source product released under the Apache 2.0 license (see either [the Apache site](https://www.apache.org/licenses/LICENSE-2.0) or the [LICENSE.txt file](LICENSE.txt)). The Apache 2.0 license allows you to freely use, modify, distribute, and sell your own products that include Apache 2.0 licensed software.
+
+We respect intellectual property rights of others and we want to make sure all incoming contributions are correctly attributed and licensed. A Developer Certificate of Origin (DCO) is a lightweight mechanism to do that.
+
+The DCO is a declaration attached to every contribution made by every developer. In the commit message of the contribution, the developer simply adds a `Signed-off-by` statement and thereby agrees to the DCO, which you can find below or at [DeveloperCertificate.org](http://developercertificate.org/).
+
+```
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the
+    best of my knowledge, is covered under an appropriate open
+    source license and I have the right under that license to
+    submit that work with modifications, whether created in whole
+    or in part by me, under the same open source license (unless
+    I am permitted to submit under a different license), as
+    Indicated in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including
+    all personal information I submit with it, including my
+    sign-off) is maintained indefinitely and may be redistributed
+    consistent with this project or the open source license(s)
+    involved.
+ ```
+
+We require that every contribution to OpenSearch is signed with a Developer Certificate of Origin. Additionally, please use your real name. We do not accept anonymous contributors nor those utilizing pseudonyms.
+
+Each commit must include a DCO which looks like this
+
+```
+Signed-off-by: Jane Smith <jane.smith@email.com>
+```
+
+You may type this line on your own when writing your commit messages. However, if your user.name and user.email are set in your git configs, you can use `-s` or `– – signoff` to add the `Signed-off-by` line to the end of the commit message.

NOTICE

@@ -1,5 +1,5 @@
-OpenSearch
-Copyright 2021 OpenSearch Contributors
+OpenSearch (https://opensearch.org/)
+Copyright OpenSearch Contributors
 
 This product includes software developed by
 Elasticsearch (http://www.elastic.co).