Add contributing guide

Author: godotalgorithm

CONTRIBUTING.rst

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+=====================
+Contributing to MOPAC
+=====================
+
+MOPAC is an open source project and, as such, contributions are welcome and appreciated.
+The standard, minimal legal stipulations apply: all contributions must be provided under
+the Apache 2.0 license and all contributors must agree to the DCO by using their real name
+and a valid email address in their git commit statements.
+
+How to contribute
+=================
+
+Please create a GitHub `Issue <https://github.com/openmopac/openmopac.github.io/issues/new>`_ for bug
+reports and feature requests.
+
+The preferred method of code contribution is to fork the project on
+`GitHub <https://github.com/openmopac/openmopac.github.io>`_, make your changes in a feature branch
+starting from the main branch, and then create a pull request.
+
+Open pull requests are also welcome, where a pull request is made before a contribution
+is ready to be merged, to open up an active dialogue between the core developers and the
+contributor about details of the contribution in development. This mode of operation is
+particularly useful when a pull request is linked with an issue articulating a problem
+that the pull request intends to solve.
+
+The Hugo-based website can be deployed from a fork by setting the build and deployment source to
+GitHub Actions in the Pages section of the repository Settings. The website rebuilds on push or trigger.
+
+What to contribute
+==================
+
+Most of the MOPAC website content is contained in the old manual and reference data webpages that
+were originally developed with Microsoft Frontpages or custom DOS scripts. Some of this information is
+out of date, and it is all embedded directly in static HTML rather than a modern format that separates
+content from style.
+
+The two long-term goals of MOPAC website development are to update old information and move content into
+the Hugo-based website. Contributions to these goals are welcome.
+
+The non-Hugo web content is located in the
+`static folder<https://github.com/openmopac/openmopac.github.io/tree/main/static>`_,
+a separate `manual repository<https://github.com/openmopac/Manual>`_,
+and a separate `reference data repository<https://github.com/openmopac/PM7_and_PM6-D3H4_accuracy>`_.
+
+Developer Certificate of Origin
+===============================
+
+Contributors to MOPAC are assumed to agree with the Linux Foundation's 
+`Developer Certificate of Origin <https://developercertificate.org/>`::
+
+    Developer Certificate of Origin
+    Version 1.1
+    
+    Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+    1 Letterman Drive
+    Suite D4700
+    San Francisco, CA, 94129
+    
+    Everyone is permitted to copy and distribute verbatim copies of this
+    license document, but changing it is not allowed.
+    
+    
+    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.