Add PHP form button block class code template description

[VitaliyBoyko]

Description (*)

Describe the purpose of the PHP form button block class code template and containing variables. (Editor > File and Code templates)

See the example here #50

[m2-assistant]

Hi @VitaliyBoyko. Thank you for your report.
To help us process this issue please make sure that you provided sufficient information.

Please, add a comment to assign the issue: @magento I am working on this

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[drpayyne]

@magento I am working on this