IE11 transpile is not documented

[mvysny]

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I would like to test my application in dev mode in IE11 but I get the message

To test your app with this browser, enable transpilation in development mode.

Transpilation can be enabled by setting the vaadin.devmode.transpile=true property for the deployment configuration using an application or a system property.

This should be documented in the documentation: what the transpilation is, why should I enable it, and how to enable it (e.g. where to add the vaadin.devmode.transpile setting - probably application.properties in case of a Spring project?). Also mention that transpilation only works in (p)npm mode - in compatibility mode it's not possible to use IE11 in dev env.

This information should be mentioned in a page dedicated for IE11, or alternatively here: https://vaadin.com/docs/v14/flow/introduction/introduction-compatibility.html