Improve drush shell command so it does the right thing when no site-i…

…nstalled drush

cmd/ddev/cmd/dotddev_assets/commands/web/README.txt

@@ -1,7 +1,4 @@
 #ddev-generated
-Scripts in this directory will be executed inside the web
-container. You can copy the example file or just rename it:
-`mv drush.example drush`, for example, and it will become
-a live command.
+Scripts in this directory will be executed inside the web container.
 
 See https://ddev.readthedocs.io/en/stable/users/extend/custom-commands/#environment-variables-provided for a list of environment variables that can be used in the scripts.

cmd/ddev/cmd/global_dotddev_assets/commands/web/README.txt

@@ -1,7 +1,7 @@
 #ddev-generated
 Scripts in this directory will be executed inside the web
 container. You can copy the example file or just rename it:
-`mv drush.example drush`, for example, and it will become
+`mv reload-nginx.example reload-nginx`, for example, and "ddev reload-nginx" will become
 a live command.
 
 See https://ddev.readthedocs.io/en/stable/users/extend/custom-commands/#environment-variables-provided for a list of environment variables that can be used in the scripts.

cmd/ddev/cmd/global_dotddev_assets/commands/web/drush

@@ -6,4 +6,8 @@
 ## Example: "ddev drush uli" or "ddev drush sql-cli" or "ddev drush --version"
 ## ProjectTypes: drupal7,drupal8,drupal9,backdrop
 
+if ! command -v drush >/dev/null; then
+  echo "drush is not available. You may need to 'ddev composer require drush/drush'"
+  exit 1
+fi
 drush "$@"