This update clarifies the process for adding a signature within the HTML editor. Previously, users were instructed to 'Insert your signature from Sign'. Now, the system prompts users to 'Insert your handwritten signature', providing a more intuitive and accurate description of the expected input.

Purpose of this PR:

- Replace 'Insert your signature from Sign' with 'Insert your handwritten signature'.

task-6217718

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Forward-Port-Of: odoo/odoo#267995