add CONTRIBUTING.md

* add Contributing section to README.
* solves spdx#30
Signed-off-by: Aviral Verma <aviral1701@gmail.com>

CONTRIBUTING.md

@@ -0,0 +1,25 @@
+Contributing
+============
+Thank you for your interest in `tools-python`. The project is open-source software, and bug reports, suggestions, and most especially patches are welcome.
+
+Issues
+------
+`tools-python` has a [project page on GitHub](https://github.com/spdx/tools-python/) where you can [create an issue](https://github.com/spdx/tools-python/issues/new) to report a bug, make a suggestion, or propose a substantial change or improvement that you might like to make. You may also wish to contact the SPDX working group technical team through its mailing list, [spdx-tech@lists.spdx.org](mailto:spdx-tech@lists.spdx.org).
+
+If you would like to work on a fix for any issue, please assign the issue to yourself prior to creating a patch.
+
+Patches
+-------
+The source code for `tools-python` is hosted on [github.com/spdx/tools-python](https://github.com/spdx/tools-python). Please review [open pull requests](https://github.com/spdx/tools-python/pulls) before committing time to a substantial revision. Work along similar lines may already be in progress.
+
+To submit a patch via GitHub, fork the repository, create a topic branch from `master` for your work, and send a pull request when ready. If you would prefer to send a patch or grant access to pull from your own Git repository, please contact the project's contributors by e-mail.
+
+To contribute an implementation of a feature defined by a version of the SPDX specification later than the one supported by the current SPDX Tools release, clone the branch `spec/X.X`, where X.X is the major.minor version of the targeted specification (e.g. "3.0").
+
+Once implemented, submit a pull request with `spec/X.X` branch as the parent branch.
+
+
+
+Licensing
+---------
+However you choose to contribute, please confirm in a comment to your pull request or by e-mail that you license your contributions under the terms of [the Apache License, Version 2.0](http://spdx.org/licenses/Apache-2.0).

README.md

@@ -27,6 +27,10 @@ Pypi: https://pypi.python.org/pypi/spdx-tools
 [Apache-2.0](LICENSE)
 
 
+# Contributing
+See the file CONTRIBUTING.md for information on making contributions to the SPDX tools-python.
+
+
 # Features
 
 * API to create and manipulate SPDX documents.