Create CLA.md

Author: cells-fileformat

.github/CLA.md

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+Contributor License Agreement (CLA)
+
+By submitting a contribution to this project, you agree that:
+1. You grant the project maintainer(s) the necessary rights to use, modify, and distribute your contribution.
+2. Your contribution is your original work or that of your employer, and you have the right to license it.
+3. This agreement applies to all future contributions unless explicitly withdrawn in writing.
+
+Signed: <Contributor's GitHub Username>