add warning in spanner db doc (#3812) (#2330)

Co-authored-by: Edward Sun <[email protected]>
Signed-off-by: Modular Magician <[email protected]>

Co-authored-by: Edward Sun <[email protected]>

Author: modular-magician

.changelog/3812.txt

@@ -0,0 +1,3 @@
+```release-note:none
+
+```

website/docs/r/spanner_database.html.markdown

@@ -31,6 +31,8 @@ To get more information about Database, see:
 * How-to Guides
     * [Official Documentation](https://cloud.google.com/spanner/)
 
+~> **Warning:** It is strongly recommended to set `lifecycle { prevent_destroy = true }` on databases in order to prevent accidental data loss. See [Terraform docs](https://www.terraform.io/docs/configuration/resources.html#prevent_destroy) for more information on lifecycle parameters.
+
 <div class = "oics-button" style="float: right; margin: 0 0 -15px">
   <a href="https://console.cloud.google.com/cloudshell/open?cloudshell_git_repo=https%3A%2F%2Fgithub.com%2Fterraform-google-modules%2Fdocs-examples.git&cloudshell_working_dir=spanner_database_basic&cloudshell_image=gcr.io%2Fgraphite-cloud-shell-images%2Fterraform%3Alatest&open_in_editor=main.tf&cloudshell_print=.%2Fmotd&cloudshell_tutorial=.%2Ftutorial.md" target="_blank">
     <img alt="Open in Cloud Shell" src="//gstatic.com/cloudssh/images/open-btn.svg" style="max-height: 44px; margin: 32px auto; max-width: 100%;">