DashboardBuilders: clarify that issue body should contain hostname

The hostname value is needed in the subsequent steps. Make it clear
that it needs to be included in the issue body.

Change-Id: I4a5a98e61bebef45c835da8ce0bd95185d56af69
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/561815
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: dmitshur

DashboardBuilders.md

@@ -74,7 +74,7 @@ The LUCI system requires builders to run two applications which authenticate to
 
   1. [Create an issue](https://github.com/golang/go/issues/new?labels=new-builder&title=x%2Fbuild%3A+add+LUCI+%3Cos-arch%3E+builder) on the Go Issue tracker requesting the addition of a new builder and assign it yourself.
      1. The title of the issue should be in the format: `x/build: add LUCI <os-arch> builder`.
-     1. Choose a hostname.
+     1. Choose a hostname and state its value in the issue body.
      1. Add the label "new-builder". (You can post a comment on the issue stating `@gopherbot, please add label new-builder.` in the issue to have [gopherbot](https://go.dev/wiki/gopherbot) add it for you.)
 
   1. Use `golang.org/x/build/cmd/genbotcert` to generate both a certificate signing request (_hostname_.csr) and a TLS private key (_hostname_.key) using the hostname (chosen beforehand) as input. Add a .txt file extension to the certificate signing request (_hostname_.csr.txt) and attach it to the GitHub issue. A team member will attach the resulting certificate (_hostname_.cert) to the GitHub issue.