Created Preparation for update with database schema changes (markdown)

Preparation-for-update-with-database-schema-changes.md

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+![Plan Header](https://puu.sh/AXSg7/5f2f78c06c.jpg)
+
+# Preparation for update with database schema changes
+
+If an update has backwards incompatible database schema changes it is mentioned in the change log.
+
+- Backup your database
+- Stop all servers
+- Start one server with Plan and wait until Patching has completed (`"All database patches applied successfully."`)
+
+If you need a rough estimate how long patching will take, you can run query `SELECT COUNT(*) as row_count FROM <table name mentioned in change log>` and estimate.  
+Patching the database usually takes ~1 second per 20000 rows of data.
+
+## How to Backup your database
+
+### SQLite
+
+- Stop your server
+- Go to Plan plugin directory
+- Make sure that `database.db-shm` and `database.db-wal` files are not present
+  - If they are the server didn't shut down properly, restart the server and stop it.
+- Copy `database.db` to your backup folder
+
+<details>
+<summary>How to restore if something goes wrong</summary>
+
+- Stop your server
+- Go to Plan plugin directory
+- Make sure that `database.db-shm` and `database.db-wal` files are not present
+  - If they are the server didn't shut down properly, restart the server and stop it.
+- Copy `database.db` to your Plan folder from your backup'
+
+</details>
+
+### MySQL
+
+- https://dev.mysql.com/doc/refman/8.0/en/mysqldump.html
+- `mysqldump [login options] <plan database name> > backup-plan-dump.sql`
+- Copy the dump file to your backup folder
+
+
+<details>
+<summary>How to restore if something goes wrong</summary>
+
+- Login to mysql
+- `mysql> drop database <broken plan database>;`
+- `mysql> source /path/to/backup-plan-dump.sql`
+
+</details>