chore: point documentation to README

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

README.md

@@ -19,6 +19,49 @@ This makes the app useful for internal directories, support operations, partner
 
 The public API contract for this app is published as [openapi-full.json](https://github.com/LibreCodeCoop/profile_fields/blob/main/openapi-full.json).
 
+## Data backup and import
+
+Run the app commands from the Nextcloud stack root, not from the host PHP environment.
+
+Export the current Profile Fields catalog and stored values:
+
+```bash
+docker compose exec -u www-data -w /var/www/html nextcloud \
+	php occ profile_fields:data:export \
+	--output=/tmp/profile_fields-export.json
+```
+
+Validate an import payload without writing anything:
+
+```bash
+docker compose exec -u www-data -w /var/www/html nextcloud \
+	php occ profile_fields:data:import \
+	--input=/tmp/profile_fields-export.json \
+	--dry-run
+```
+
+Apply the non-destructive `upsert` import:
+
+```bash
+docker compose exec -u www-data -w /var/www/html nextcloud \
+	php occ profile_fields:data:import \
+	--input=/tmp/profile_fields-export.json
+```
+
+Notes:
+
+- The import contract is versioned with `schema_version` and reconciles definitions by `field_key` and values by `field_key + user_uid`.
+- The first delivery is non-destructive: missing items in the payload do not delete existing definitions or values.
+- Validation is all-or-nothing. If the payload contains an incompatible definition or a missing destination user, no database write is performed.
+- For a restore in the same environment, clear app data explicitly before reimporting:
+
+```bash
+docker compose exec -u www-data -w /var/www/html nextcloud \
+	php occ profile_fields:data:clear \
+	--definitions \
+	--force
+```
+
 ## Screenshots
 
 ![Admin catalog](img/screenshots/admin-catalog.png)