Add migration documentation.

docs/configure.md

@@ -76,6 +76,8 @@ storage:
       username: ma1sd
       password: secret_password
 ```
+See [the migration instruction](migration-to-postgresql.md) from sqlite to postgresql
+
 
 ## Logging
 ```yaml

docs/migration-to-postgresql.md

@@ -0,0 +1,41 @@
+# Migration from sqlite to postgresql
+
+Starting from the version 2.3.0 ma1sd support postgresql for internal storage in addition to sqlite (parameters `storage.backend`).
+
+#### Migration steps
+
+1. create the postgresql database and user for ma1sd storage
+2. create a backup for sqlite storage (default location: /var/lib/ma1sd/store.db)
+3. migrate data from sqlite to postgresql
+4. change ma1sd configuration to use the postgresql
+
+For data migration is it possible to use https://pgloader.io tool.
+
+Example of the migration command:
+```shell script
+pgloader --with "quote identifiers" /path/to/store.db pgsql://ma1sd_user:ma1sd_password@host:port/database
+```
+or (short version for database on localhost)
+```shell script
+pgloader --with "quote identifiers" /path/to/store.db pgsql://ma1sd_user:ma1sd_password@localhost/ma1sd
+```
+
+An option `--with "quote identifies"` used to create case sensitive tables.
+ma1sd_user - postgresql user for ma1sd.
+ma1sd_password - password of the postgresql user.
+host - postgresql host
+post - database port (default 5432)
+database - database name.
+
+
+Configuration example for postgresql storage:
+```yaml
+storage:
+  backend: postgresql
+  provider:
+    postgresql:
+      database: '//localhost/ma1sd' # or full variant //192.168.1.100:5432/ma1sd_database
+      username: 'ma1sd_user'
+      password: 'ma1sd_password'
+```
+