Improve `#AnkiWebConflicts`

[david-allison]

https://docs.ankidroid.org/#AnkiWebConflicts could be improved in a number of ways

At least:

• Link to https://docs.ankiweb.net/syncing.html#conflicts
• Better improve explaining 'AnkiWeb' and 'AnkiDroid' buttons

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• Ref: Add 'Help' icon for sync conflict Anki-Android#17544 (comment)