Create registering IRIs.md

Moved the IRI registration instructions to a more specifically named file so the README can be used for more general contributor instructions.

Author: APCox

documentation/contributing/registering IRIs.md

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+## Instructions for Registering new IRIs in CCO
+
+Before creating a pull request containing a new CCO term, developers must register the new IRIs in the csv file maintained exclusively on this separate [branch](https://github.com/CommonCoreOntology/CommonCoreOntologies/tree/iri-registry-branch/). 
+
+To that end: 
+
+1. Navigate to this [directory](https://github.com/CommonCoreOntology/CommonCoreOntologies/tree/iri-registry-branch/documentation/contributing) on the IRI Registry branch.
+2. Open the file `iri-registry.csv` located there and navigate to the bottom row of the file.
+3. In the next empty row, add the new IRI(s) as an increment from the last one. Also add your name, the date, and the associated issue number(s).
+4. Commit your changes directly to the IRI Registry Branch and push to origin.
+6. Now you can open a new branch off of `develop` to execute your work using the IRIs that you have registered.