Recover doc for appveyor project ID

Cherry-picked from f59eb30bbb9f1c30dcbfebe54aed72e1f51ba7cc which failed
to update the book and was replaced in
1271bb4de0c0e0a085be239c2418af9c673ffc87.

diff --git a/src/doc/src/reference/manifest.md b/src/doc/src/reference/manifest.md
index b8f746956705ba18e5719b78676c1f2efb956cab..5f5ac6a9871a88f3f1caaf93ffbe876435c460ca 100644 (file)
--- a/src/doc/src/reference/manifest.md
+++ b/src/doc/src/reference/manifest.md
@@ -199,7 +199,8 @@ license-file = "..."
 
 # Appveyor: `repository` is required. `branch` is optional; default is `master`
 # `service` is optional; valid values are `github` (default), `bitbucket`, and
-# `gitlab`.
+# `gitlab`; `id` is optional; you can specify the appveyor project id if you
+# want to use that instead.
 appveyor = { repository = "...", branch = "master", service = "github" }
 
 # Circle CI: `repository` is required. `branch` is optional; default is `master`