Update contribution guide and issue/PR templates

Author: Shauheen Zahirazami

CONTRIBUTING.md

@@ -1,3 +1,26 @@
+# First things first: Welcome!
+
+If you are here, it means you are interested in helping us out. A hearty welcome and thank you! We always welcome new contribution to any of the following areas:
+* Bug reports regarding the software or the documentation.
+* Documentation updates, tutorial and examples.
+* New code to implement a feature or patch an issue.
+
+## Getting started:
+
+Please join the community on [gitter](https://gitter.im/dotnet). Also please make sure to take a look at the project [roadmap](ROADMAP.md).
+
+### Pull requests
+
+If you are new to GitHub [here](https://help.github.com/categories/collaborating-with-issues-and-pull-requests/) is a detailed help source on getting involved with development on GitHub.
+
+As a first time contributor, you will be invited to sign the Contributor License Agreement (CLA). Please follow the instructions of the dotnet foundation bot reviewer on your PR to sign the agreement. Please note that only original code with signed CLA could be merged into the main repo.
+
+Your pull request needs to reference a filed issue. Please fill in the template that is populated for the pull request. Only pull requests adressing small typos can have no issues associated with them.
+
+An ML.NET team member will be assigned to your pull request once the continuous integration checks have passed successfully.
+
+All commits in a pull request will be squashed to a single commit with the original creator as author.
+
 # Contributing
 
 See [Contributing](Documentation/project-docs/contributing.md) for information about coding styles, source structure, making pull requests, and more.

ISSUE_TEMPLATE.md

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+If you are filing an issue on GitHub, please ensure that it is a bug or a feature request or a major issue with the documentation. Also please take the time to fill out this form:
+
+### System information
+
+- **OS Platform and Distribution**:
+- **dot net version**: 
+- **Exact steps to reproduce**:
+
+### Describe the problem
+
+Please use as much details as possible to explain why this is a bug or a feature request.
+
+### Source code / logs
+
+Please provide the code or logs or traces that would be helpful to diagnose the issue you are reporting.

PULL_REQUEST_TEMPLATE.md

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+Please ensure that the title for the pull request is meaningful and includes exactly what was done. Your pull request needs to reference a filed issue. Only pull requests adressing small typos can have no issues associated with them. Please use the following template:
+
+```
+Issue #ISSUE_NUMBER THE_TITLE_OF_THE_PULL_REQUEST
+ 
+This addressed the issue by 
+  * INSERT_DESCRIPTION_OF_SOMETHING
+  * INSERT_DESCRIPTION_OF_SOMETHING_ELSE
+  * ...
+ 
+Issues:
+  If your PR is addressing multiple issues, then list them all here.
+  This closes #ISSUE_NUMBER
+  This fixes #ISSUE_NUMBER
+```