duplicacy: add page (#6598)

pages/common/duplicacy.md

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+# duplicacy
+
+> A lock-free deduplication cloud backup tool.
+> More information: <https://github.com/gilbertchen/duplicacy/wiki>.
+
+- Use current directory as the repository, initialize a SFTP storage and encrypt the storage with a password:
+
+`duplicacy init -e {{snapshot_id}} {{sftp://user@192.168.2.100/path/to/storage/}}`
+
+- Save a snapshot of the repository to the default storage:
+
+`duplicacy backup`
+
+- List snapshots of current repository:
+
+`duplicacy list`
+
+- Restore the repository to a previously saved snapshot:
+
+`duplicacy restore -r {{revision}}`
+
+- Check the integrity of snapshots:
+
+`duplicacy check`
+
+- Add another storage to be used for the existing repository:
+
+`duplicacy add {{storage_name}} {{snapshot_id}} {{storage_url}}`
+
+- Prune a specific revision of snapshot:
+
+`duplicacy prune -r {{revision}}`
+
+- Prune revisions, keeping one revision every `n` days for all revisions older than `m` days:
+
+`duplicacy prune -keep {{n:m}}`