feat: add upgrade guide (tauri-apps#1340)

* feat: add upgrade guide

* update paragraph

Signed-off-by: Lorenzo Lewis <lorenzo_lewis@icloud.com>

* lots of updates

Signed-off-by: Lorenzo Lewis <lorenzo_lewis@icloud.com>

* refactors

Signed-off-by: Lorenzo Lewis <lorenzo_lewis@icloud.com>

* add link to migrate cli command

Signed-off-by: Lorenzo Lewis <lorenzo_lewis@icloud.com>

* add examples

* change high-level phrasing to upgrade

Signed-off-by: GitHub <noreply@github.com>

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Signed-off-by: Lorenzo Lewis <lorenzo_lewis@icloud.com>
Signed-off-by: GitHub <noreply@github.com>
Co-authored-by: Lorenzo Lewis <lorenzo_lewis@icloud.com>

Author: 2 people