[Docs] Database preparation: Clarify why database client is installed on Gitea server (#12833)

* Database preparation: Clarify why database client is installed on Gitea server

The database client program (`mysql` or `psql`) is used to test database
connection, but Gitea use Go's database driver to do the same.

Also, rename "server part" and "client part" to "server application" and
"client program" to disambiguate.

* Update docs/content/doc/installation/database-preparation.en-us.md

Co-authored-by: 6543 <6543@obermui.de>

docs/content/doc/installation/database-preparation.en-us.md

@@ -19,7 +19,7 @@ You need a database to use Gitea. Gitea supports PostgreSQL, MySQL, SQLite, and
 
 Database instance can be on same machine as Gitea (local database setup), or on different machine (remote database).
 
-Note: All steps below requires that the database engine of your choice is installed on your system. For remote database setup, install the server part on database instance and client part on your Gitea server. In addition, make sure you use same engine version for both server and client for some engine features to work. For security reason, protect `root` (MySQL) or `postgres` (PostgreSQL) database superuser with secure password. The steps assumes that you run Linux for both database and Gitea servers.
+Note: All steps below requires that the database engine of your choice is installed on your system. For remote database setup, install the server application on database instance and client program on your Gitea server. The client program is used to test connection to the database from Gitea server, while Gitea itself use database driver provided by Go to accomplish the same thing. In addition, make sure you use same engine version for both server and client for some engine features to work. For security reason, protect `root` (MySQL) or `postgres` (PostgreSQL) database superuser with secure password. The steps assumes that you run Linux for both database and Gitea servers.
 
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