Major GUIDE rework

GUIDE.md

@@ -6,9 +6,29 @@ To make maintainers & users life easier `dbump` keeps database-specific migrator
 This makes `go.mod` clean or even empty and simplifies security audit.
 
 To find what database are supported see `dbump_*` directories in root:
-* ClickHouse (TODO: link)
-* MySQL (TODO: link)
-* Postgres (TODO: link for pg & pgx)
+| Database | Go module  | Link  |
+|---|---|---|
+| ClickHouse     | `github.com/cristalhq/dbump/dbump_ch`      | [dbump_ch](https://github.com/cristalhq/dbump/tree/main/dbump_ch)
+| Mongo          | `github.com/cristalhq/dbump/dbump_mongo`   | [dbump_mongo](https://github.com/cristalhq/dbump/tree/main/dbump_mongo)
+| MySQL          | `github.com/cristalhq/dbump/dbump_mysql`   | [dbump_mysql](https://github.com/cristalhq/dbump/tree/main/dbump_mysql)
+| MS SQL         | `github.com/cristalhq/dbump/dbump_mssql`   | [dbump_mssql](https://github.com/cristalhq/dbump/tree/main/dbump_mssql)
+| Postgres       | `github.com/cristalhq/dbump/dbump_pg`      | [dbump_pg](https://github.com/cristalhq/dbump/tree/main/dbump_pg)
+| Postgres (pgx) | `github.com/cristalhq/dbump/dbump_pgx`     | [dbump_pgx](https://github.com/cristalhq/dbump/tree/main/dbump_pgx)
+| GCP Spanner    | `github.com/cristalhq/dbump/dbump_spanner` | [dbump_spanner](https://github.com/cristalhq/dbump/tree/main/dbump_spanner)
+
+Just do: `go get github.com/cristalhq/dbump/dbump_XXX` with a specific `XXX` and you will be able to run migrations for this database.
+
+## Migration modes
+
+| Mode | Description |
+|---|---|
+| ModeNotSet  | Default value in config, should not be used.
+| ModeUp      | Apply all the migrations that weren't applied yet.
+| ModeDown    | Revert all the migrations that were applied.
+| ModeUpOne   | Apply only 1 migration.
+| ModeDownOne | Revert only current migration.
+| ModeRedo    | Revert and apply again current migration.
+| ModeDrop    | Revert all migrations and remove `dbump` table.
 
 ## ZigZag mode
 
@@ -28,3 +48,22 @@ Steps 1 is obvious but doing 2,3 verifies that migration can clean after itself
 
 Credits goes to [Postgres.ai](https://postgres.ai/) mentioning this feature at conference.
 
+## Do not take database locks
+
+If for some reason you don't want or you can't take lock on database (why???) there is `AsLocklessMigrator` function to achieve this:
+
+```go
+// let's take Postgres for example 
+m := dbump_pg.NewMigrator(...)
+
+// volia, now m is a migrator that will not take a lock
+m = dbump.AsLocklessMigrator(m)
+
+// pass m in config param as before
+dbump.Run(...)
+```
+
+However, lock prevents from running few migrators at once, possible creating bad situations that's is hard to fix.
+
+Also, not all migrators supports locks.
+