Merge pull request COMCIFS#11 from vaitkus/add-readme

Add README.md

Author: jamesrhester

README.md

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+[![CIF syntax check](https://github.com/COMCIFS/Restraints_Dictionary/actions/workflows/main.yml/badge.svg)](https://github.com/COMCIFS/Restraints_Dictionary/actions)
+
+# Restraints Dictionary (rstrCIF)
+
+CIF data item definitions for description of restraints or constraints applied in least-squares refinement of crystal structures.
+
+## Warning
+
+[This dictionary](cif_rstr.dic) is the latest **draft** version.
+Definitions are subject to change and software should be careful not to hard-code information.
+The latest approved restraints dictionary is available from the [IUCr CIF website](https://www.iucr.org/resources/cif/dictionaries).
+
+## Contributing
+
+Contributions are very welcome, both from least-squares refinement experts and people with technical CIF knowledge.
+Ways of contributing include:
+
+1. Raising an issue, including suggesting a new data name (see "Issues" tab above).
+2. Creating a pull request with suggested improvements to the dictionary.
+3. Commenting on already existing issues.
+4. Reviewing pull requests.
+
+If the "Github way" is not familiar to you, we suggest looking at [some closed issues](https://github.com/COMCIFS/Restraints_Dictionary/issues?q=is%3Aissue+is%3Aclosed) and [some closed pull requests](https://github.com/COMCIFS/Restraints_Dictionary/issues?q=is%3Apr+is%3Aclosed) to see how the process works.
+You may also find [this wiki entry](https://github.com/COMCIFS/cif_core/wiki/Getting-started-with-Github-and-Git-for-development-of-CIF-dictionaries) helpful.
+
+## Update guidelines
+
+In general, any changes to the semantic content of the dictionary should be presented as a pull request.
+Someone other than the author of the original pull request should merge the pull request once they are satisfied that the pull request is suitable for inclusion.
+This protocol is not necessary for changes to the layout of the dictionary  that do not change the meaning of any data names.