Auto merge of #9674 - iankronquist:patch-1, r=alexcrichton

Document cargo limitation w/ workspaces & configs

This behavior is described in this bug:
#2930

I think we should document limitations of the tool which exist at present if they do not bind our hands in the future.
If this bug is fixed, this note should be removed.

Author: bors

src/doc/src/reference/config.md

@@ -30,6 +30,14 @@ together. Numbers, strings, and booleans will use the value in the deeper
 config directory taking precedence over ancestor directories, where the
 home directory is the lowest priority. Arrays will be joined together.
 
+At present, when being invoked from a workspace, Cargo does not read config
+files from crates within the workspace. i.e. if a workspace has two crates in
+it, named `/projects/foo/bar/baz/mylib` and `/projects/foo/bar/baz/mybin`, and
+there are Cargo configs at `/projects/foo/bar/baz/mylib/.cargo/config.toml`
+and `/projects/foo/bar/baz/mybin/.cargo/config.toml`, Cargo does not read
+those configuration files if it is invoked from the workspace root
+(`/projects/foo/bar/baz/`).
+
 > **Note:** Cargo also reads config files without the `.toml` extension, such as
 > `.cargo/config`. Support for the `.toml` extension was added in version 1.39
 > and is the preferred form. If both files exist, Cargo will use the file