Add Cloud Synchronization page

Cloud-Synchronization.md

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+It is not planned to integrate the cloud APIs directly to KeePass DX because it would be necessary to integrate each client one by one and not only the knowns (incidentally could cause security breaches and are not necessarily under free license with open code).
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+**KeePass DX App** will remain offline but **will communicate with a separate file manager or cloud clients that can be online**. The goal is to encapsulate the components and stay in the philosophy of free software.
+Data synchronization has not been developed yet but is planned.
+In order to have the most complete visibility of online services that work with KeePass DX, you can leave comments to indicate if your file manager or cloud client is fully working or not depending of Android and KeePass DX version.
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+| File manager / Cloud Client  | Works | Pros | Cons | Officially tested
+| --- | --- | --- | -------- | --- |
+| Direct http / https/ ftp link | **Not directly**, only  *content://* and *file://* are directly supported in the app, you have to go through an online file manager to access files by these online protocols | - | - | Yes
+| NextCloud App | - | Source code open, Free license | More difficult to set up for a private server | No
+| OwnCloud App | Partially | Source code open, Free license | More difficult to set up for a private server | No
+| Google Drive App | Partially, the recovered file name is not correct, synchronization is not done. #172 | Easy to use | Unopened source code, proprietary license | No
+| Dropbox App | - | - | - | No
+| OneDrive App | - | - | - | No
+| PCloud App | - | - | - | No
+| Teamdrive | - | - | - | No