chore: document ci-mirrors

Author: marcoieni

service-catalog/README.md

@@ -12,12 +12,14 @@ how-to guides, explanations, and reference documentation.
 
 - [bastion](./bastion/README.md)
 - [bors](./bors/README.md)
+- [ci-mirrors](./ci-mirrors/README.md)
 - [crater](./crater/README.md)
 - [crates-io](./crates-io/README.md)
 - [dev-desktops](./dev-desktops/README.md)
 - [discord-mods-bot](./discord-mods-bot/README.md)
 - [dns](./dns/README.md)
 - [docs-rs](./dns/README.md)
+- [infra-smoke-tests](./dns/README.md)
 - [monitorbot](./monitorbot/README.md)
 - [playground](./playground/README.md)
 - [releases](./releases/README.md)

service-catalog/ci-mirrors/README.md

@@ -0,0 +1,11 @@
+# CI Mirrors
+
+The Rust Project mirrors some files in `ci-mirrors.rust-lang.org`, which is a
+[CDN](https://github.com/rust-lang/simpleinfra/blob/30a701eebbf0dea1fcd9a49104d9b9908a9929cc/terraform/shared/static-websites.tf#L9) serving
+the contents of the
+[rust-lang-ci-mirrors](https://github.com/rust-lang/simpleinfra/blob/30a701eebbf0dea1fcd9a49104d9b9908a9929cc/terraform/shared/s3.tf#L69)
+S3 bucket.
+
+To mirror a new file, add it to the
+[ci-mirrors](https://github.com/rust-lang/ci-mirrors/blob/fc9221d92847e49c277a2099a263cc902699fa9b/files.toml#L1)
+repository.