[CONTRIBUTING] Improve CLA information

Improve CLA information to adhere to Google policies.

.github/CONTRIBUTING.md

@@ -168,15 +168,17 @@ While the prerequisites above must be satisfied prior to having your pull reques
 
 ### Contributor License Agreement
 
-Contributions to this project must be accompanied by a Contributor License
-Agreement. You (or your employer) retain the copyright to your contribution,
-this simply gives us permission to use and redistribute your contributions as
-part of the project. Head over to <https://cla.developers.google.com/> to see
-your current agreements on file or to sign a new one.
+Contributions to this project must be accompanied by a
+[Contributor License Agreement](https://cla.developers.google.com/about) (CLA).
+You (or your employer) retain the copyright to your contribution; this simply
+gives us permission to use and redistribute your contributions as part of the
+project.
 
-You generally only need to submit a CLA once, so if you've already submitted one
-(even if it was for a different project), you probably don't need to do it
-again.
+If you or your current employer have already signed the Google CLA (even if it
+was for a different project), you probably don't need to do it again.
+
+Visit <https://cla.developers.google.com/> to see your current agreements or to
+sign a new one.
 
 ## Styleguides
 

CHANGELOG.md

@@ -23,6 +23,7 @@
 ### Development
 
 - license: Correct LICENSE file @Ana06
+- documentation: Improve CLA information in CONTRIBUTING @Ana06
 
 ### Raw diffs
 - [capa v8.0.1...master](https://github.com/mandiant/capa/compare/v8.0.1...master)