Improve docs about certificates when enabling TLS for Gitaly nodes

In order to configure Gitaly to communicate via TLS, its certificate
needs to be installed to all Gitaly nodes including itself as well as
all off its clients. The paragraph mentioning this is confusingly
worded, making it easy to miss its intention.

Reword the paragraph to make its intention clearer.

doc/administration/gitaly/index.md

@@ -415,9 +415,9 @@ with a Gitaly instance that listens for secure connections you will need to use
 scheme in the `gitaly_address` of the corresponding storage entry in the GitLab configuration.
 
 You will need to bring your own certificates as this isn't provided automatically.
-The certificate to be used needs to be installed on all Gitaly nodes, and the
-certificate (or CA of certificate) on all
-client nodes that communicate with it following the procedure described in
+The certificate, or its certificate authority, must be installed on all Gitaly
+nodes (including the Gitaly node using the certificate) and on all client nodes
+that communicate with it following the procedure described in
 [GitLab custom certificate configuration](https://docs.gitlab.com/omnibus/settings/ssl.html#install-custom-public-certificates).
 
 NOTE: **Note**