Adding API Docs for CA Pool (#13720) (#22426)

[upstream:8b669853b9fdc908c7b29815686a953b1280ef83]

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

website/docs/r/privateca_ca_pool.html.markdown

@@ -26,6 +26,11 @@ issuance policies for one or more CertificateAuthority resources and to rotate C
 trust anchor.
 
 
+To get more information about CaPool, see:
+
+* [API documentation](https://cloud.google.com/certificate-authority-service/docs/reference/rest/v1/projects.locations.caPools)
+* How-to Guides
+    * [Certificate Authority Service Overview](https://cloud.google.com/certificate-authority-service/docs/overview)
 
 <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_image=gcr.io%2Fcloudshell-images%2Fcloudshell%3Alatest&cloudshell_print=.%2Fmotd&cloudshell_tutorial=.%2Ftutorial.md&cloudshell_working_dir=privateca_capool_basic&open_in_editor=main.tf" target="_blank">