Improve services docs (#927)

Co-authored-by: qwerty287 <80460567+qwerty287@users.noreply.github.com>

docs/docs/20-usage/60-services.md

@@ -1,6 +1,10 @@
 # Services
 
-Woodpecker provides a services section in the YAML file used for defining service containers. The below configuration composes database and cache containers.
+Woodpecker provides a services section in the YAML file used for defining service containers.
+The below configuration composes database and cache containers.
+
+Services are accessed using custom hostnames.
+In the example below, the MySQL service is assigned the hostname `database` and is available at `database:3306`.
 
 ```diff
 pipeline:
@@ -18,8 +22,6 @@ services:
     image: redis
 ```
 
-Services are accessed using custom hostnames. In the above example the mysql service is assigned the hostname `database` and is available at `database:3306`.
-
 ## Configuration
 
 Service containers generally expose environment variables to customize service startup such as default usernames, passwords and ports. Please see the official image documentation to learn more.
@@ -77,3 +79,21 @@ services:
   database:
     image: mysql
 ```
+
+## Complete Pipeline Example
+
+```yml
+services:
+  database:
+    image: mysql
+    environment:
+      - MYSQL_DATABASE=test
+      - MYSQL_ROOT_PASSWORD=example
+pipeline:
+  get-version:
+    image: ubuntu
+    commands:
+      - ( apt update && apt dist-upgrade -y && apt install -y mysql-client 2>&1 )> /dev/null
+      - sleep 30s # need to wait for mysql-server init
+      - echo 'SHOW VARIABLES LIKE "version"' | mysql -uroot -hdatabase test -pexample
+```