Add CLA signing instructions

CONTRIBUTING.md

@@ -1,5 +1,15 @@
 # Contributing to Central64
 
+## Contributor License Agreement
+
+Before contributing any code to this project, we kindly ask you to sign a Contributor License Agreement (CLA). We can not accept any pull request if a CLA has not been signed.
+
+- If you are contributing on behalf of yourself, the CLA signature is included as a part of the pull request process.
+
+- If you are contributing on behalf of your employer, please sign our [Corporate Contributor License](https://github.com/Autodesk/autodesk.github.io/releases/download/1.0/ADSK.Form.Corp.Contrib.Agmt.for.Open.Source.docx) Agreement. The document includes instructions on where to send the completed forms to. Once a signed form has been received, we can happily review and accept your pull requests.
+
+Contributors are expected to follow the [Contributor Covenant](CODE_OF_CONDUCT.md), which describes the code of conduct for Autodesk open source projects like this one.
+
 ## Logging Issues
 
 ### Suggestions