Create README.md

Credit to audreyr/cookiecutter-pypackage for the parts on contributing.

README.md

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+# Counter-Strike: Global Offensive map overviews
+
+This is a collection of radar overviews, and eventually thumbnails,
+in more usable formats, with scripts for easily updating them.
+
+## Updating the overviews
+
+* Prepare the virtualenv:
+
+```bash
+  virtualenv virtualenv
+  . virtualenv/bin/activate
+  pip install -r requirements.txt
+```
+
+* Drop the `.dds` files from `common/Counter-Strike Global Offensive/csgo/resource/overviews` in
+`csgo-overviews/overviews/raw`.
+
+* Run the script:
+
+```bash
+  scripts/update_overviews.py
+```
+
+## Contributing
+
+Contributions are welcome, and they are greatly appreciated! Every
+little bit helps, and credit will always be given.
+
+### Report Bugs
+
+Report bugs using the [issue tracker](https://github.com/zoidbergwill/csgo-overviews/issues?state=open).
+
+If you are reporting a bug, please include:
+
+* Your operating system name and version.
+* Any details about your local setup that might be helpful in troubleshooting.
+* Detailed steps to reproduce the bug.
+
+### Fix Bugs
+
+Look through the GitHub issues for bugs. Anything tagged with "bug"
+is open to whoever wants to implement it.
+
+### Implement Features
+
+Look through the GitHub issues for features. Anything tagged with "feature"
+is open to whoever wants to implement it.
+
+### Submit Feedback
+
+The best way to send feedback is using the [issue tracker](https://github.com/zoidbergwill/csgo-overviews/issues?state=open)
+
+If you are proposing a feature:
+
+* Explain in detail how it would work.
+* Keep the scope as narrow as possible, to make it easier to implement.
+* Remember that this is a volunteer-driven project, and that contributions
+  are welcome :)