[wordpress] Document need for username/password with external db

wordpress/README.md

@@ -49,9 +49,12 @@ Then, access it via `http://localhost:8080` or `http://host-ip:8080` in a
 browser.
 
 If you'd like to use an external database instead of a linked `mysql` container,
-specify the hostname and port with `WORDPRESS_DB_HOST`:
+specify the hostname and port with `WORDPRESS_DB_HOST` along with the password
+in `WORDPRESS_DB_PASSWORD` and the username in `WORDPRESS_DB_USER` (if it is
+something other than `root`):
 
-    docker run --name some-wordpress -e WORDPRESS_DB_HOST=10.1.2.3:3306 -d wordpress
+    docker run --name some-wordpress -e WORDPRESS_DB_HOST=10.1.2.3:3306 \
+        -e WORDPRESS_DB_USER=... -e WORDPRESS_DB_PASSWORD=... -d wordpress
 
 # Supported Docker versions
 

wordpress/content.md

@@ -39,6 +39,9 @@ Then, access it via `http://localhost:8080` or `http://host-ip:8080` in a
 browser.
 
 If you'd like to use an external database instead of a linked `mysql` container,
-specify the hostname and port with `WORDPRESS_DB_HOST`:
+specify the hostname and port with `WORDPRESS_DB_HOST` along with the password
+in `WORDPRESS_DB_PASSWORD` and the username in `WORDPRESS_DB_USER` (if it is
+something other than `root`):
 
-    docker run --name some-wordpress -e WORDPRESS_DB_HOST=10.1.2.3:3306 -d wordpress
+    docker run --name some-wordpress -e WORDPRESS_DB_HOST=10.1.2.3:3306 \
+        -e WORDPRESS_DB_USER=... -e WORDPRESS_DB_PASSWORD=... -d wordpress