Update CLA content in workflow.md

Update content related to CLA, as in PR #814

Author: Amanda Butler

docs/reference/contributing/guidelines/workflow.md

@@ -1,6 +1,6 @@
 ## Workflow
 
-All code changes and additions to Mbed OS are handled through GitHub. If you want to contribute, either by adding features or by fixing bugs, please follow the guidelines for [new features](#features) and [bugs](#reporting-bugs). In both cases, please follow the [code style guide and GitHub pull request guidelines](/docs/v5.10/reference/style.html). Please also read the [Contributor License Agreement (CLA)](/docs/v5.10/reference/license.html) guidelines because we will immediately close pull requests submitted without a CLA.
+All code changes and additions to Mbed OS are handled through GitHub. If you want to contribute, either by adding features or by fixing bugs, please follow the guidelines for [new features](#features) and [bugs](#reporting-bugs). In both cases, please follow the [code style guide and GitHub pull request guidelines](/docs/v5.10/reference/style.html).
 
 ### Mbed OS maintainers