Recover doc for appveyor project_name

First added in 53012bd4df83a0d43ce7dfd0175d78b084823477 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 94680d07110399f622679c6c28045310e8671ac0..99e5965e958dd95bca2c9cff546e3e784d55dfb5 100644 (file)
--- a/src/doc/src/reference/manifest.md
+++ b/src/doc/src/reference/manifest.md
@@ -200,7 +200,8 @@ license-file = "..."
 # Appveyor: `repository` is required. `branch` is optional; default is `master`
 # `service` is optional; valid values are `github` (default), `bitbucket`, and
 # `gitlab`; `id` is optional; you can specify the appveyor project id if you
-# want to use that instead.
+# want to use that instead. `project_name` is optional; use when the repository
+# name differs from the appveyor project name.
 appveyor = { repository = "...", branch = "master", service = "github" }
 
 # Circle CI: `repository` is required. `branch` is optional; default is `master`