Add note in code so one does not forget next time

meilisearch/build.rs

@@ -1,6 +1,9 @@
 use vergen::{vergen, Config, SemverKind};
 
 fn main() {
+    // Note: any code that needs VERGEN_ environment variables should take care to define them manually in the Dockerfile and pass them
+    // in the corresponding GitHub workflow (publish_docker.yml).
+    // This is due to the Dockerfile building the binary outside of the git directory.
     let mut config = Config::default();
     // allow using non-annotated tags
     *config.git_mut().semver_kind_mut() = SemverKind::Lightweight;