feat: Add documentation about e2ee

[artonge]

@marinofaggiana @mgallien @alperozturk96 can you add screenshots for your respective platform?

Note: the android screenshots are in French, so they need to be replaced.

Fix nextcloud/end_to_end_encryption#936

[alexanderdd]

Hello, some suggestions:

• from one of your device -> from one of your devices
• "On the browser, you'll first have to enable e2ee in the browser" -> "In the browser, you'll first have to allow end to end encryption in the personal settings."
• I would put the section "encrypting a folder" right after "enabling e2ee", and put the section "adding an e2ee device" after that. IMO this better represents the most common workflow.
• in "encrypting a folder", maybe first show how to create a new folder in the client, which can then be encrypted (probably the most common use case, and users might not know that you can create folders via the ...-menu)
• in "adding an e2ee device > web" maybe add that it is currently read-only, and that these folders cannot be shared with users/groups

Thank you for this documentation!

[alperozturk96]

@artonge If these are okay I can update the PR.

e2ee-android-add

e2ee-android-mnemonic

e2ee-android-setup

[artonge]

@artonge If these are okay I can update the PR.

I would invert add and mnemonic, no?

[alperozturk96]

@artonge If these are okay I can update the PR.

I would invert add and mnemonic, no?

Ahh, yes that's right. I fixed the titles

[artonge]

Ping @mgallien @marinofaggiana

[marinofaggiana]

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