Merge pull request rails#54318 from german/add_db_system_change_command_to_doc

Added documentation for `rails db:system:change` command

Author: p8

guides/source/command_line.md

@@ -551,6 +551,30 @@ The most common commands of the `db:` rails namespace are `migrate` and `create`
 
 More information about migrations can be found in the [Migrations](active_record_migrations.html) guide.
 
+#### Switching to a Different Database Later
+
+After creating a new Rails application, you have the option to switch to any
+other supported database. For example, you might work with SQLite for a while and
+then decide to switch to PostgreSQL. In this case, you only need to run:
+
+```bash
+$ rails db:system:change --to=postgresql
+    conflict  config/database.yml
+Overwrite config/database.yml? (enter "h" for help) [Ynaqdhm] Y
+       force  config/database.yml
+        gsub  Gemfile
+        gsub  Gemfile
+...
+```
+
+And then install the missing gems:
+
+```bash
+$ bundle install
+...
+
+```
+
 ### `bin/rails notes`
 
 `bin/rails notes` searches through your code for comments beginning with a specific keyword. You can refer to `bin/rails notes --help` for information about usage.