Add comment for replace

Signed-off-by: Xuanwo <github@xuanwo.io>

Author: Xuanwo

Cargo.toml

@@ -104,4 +104,7 @@ object = { opt-level = 3 }
 rustc-demangle = { opt-level = 3 }
 
 [patch.crates-io]
+# http-types doesn't play well with the new errors api.
+# This fork address this problem, and should be removed once we upgrade to
+# new toolchain.
 http-types = { git = "https://github.com/Xuanwo/http-types", rev = "106fc6d" }