[librsvg] Note in Cargo.toml about updating BuildStream/cargo-fetcher/Cargo.lock

[Federico Mena Quintero <federico src gnome org>]

commit 2452f86d0c1bd3cc35b5628f1a6d48b9307f620b
Author: Federico Mena Quintero <federico gnome org>
Date:   Mon Apr 2 19:52:10 2018 -0500

    Note in Cargo.toml about updating BuildStream/cargo-fetcher/Cargo.lock

 rsvg_internals/Cargo.toml | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/rsvg_internals/Cargo.toml b/rsvg_internals/Cargo.toml
index fc5a3a83..92c7704f 100644
--- a/rsvg_internals/Cargo.toml
+++ b/rsvg_internals/Cargo.toml
@@ -5,6 +5,17 @@ authors = ["Federico Mena Quintero <federico gnome org>"]
 workspace = "../"
 build = "build.rs"
 
+# IMPORTANT: If you add/remove/update dependencies here, please also
+# update Cargo.toml in https://gitlab.com/BuildStream/cargo-fetcher
+# (just submit a merge request there).
+#
+# BuildStream/cargo-fetcher lets GNOME's BuildStream continuous build
+# service know which dependencies are required.
+#
+# Please update your dependencies here, then run "cargo update" to
+# regenerate librsvg/Cargo.lock, and copy the resolved version numbers
+# from there into cargo-fetcher/Cargo.toml.
+
 [build-dependencies]
 phf_codegen = "0.7.21"