[DOC] Authenticate NEAR Users Verify Step Unclear

[thisisjoshford]

Dev Feedback for Step #3 - Verify User Signature (Authenticate NEAR Users doc)

"Lots of missing variables with no context in step 3, difficult to know what's needed within the variables "

• Review the example and code snippets to resolve any mistakes and enhance clarity.

cc @andy-haynes @mpeterdev -> noting for potential NAJ helper :)