docs: Declare support level for each crate in our Charter / docs

This is to bring us into conformance with the [Rust crate ownership
policy](https://forge.rust-lang.org/policies/crate-ownership.html).

Items of note
- `cargo-credential-1password` is declared as Experimental as it is
  intended for the community but I was unsure if we wanted to commit to
  full support for it.  In my mind, the ideal thing to do would be to
  expatriate this to 1password.
- `home` is declared as Internal despite its wide use within the
  ecosystem.
- `cargo-credential` is declared as Intentional as its an API intended
  for the wider ecosystem and I didn't see a reason to declare it
  experimental.
- `cargo-platform`, `cargo-util-schemas`, and `crates-io` are declared
  as Intentional as they are both used internally and intended for
  others to use for logic that integrates with cargo/registries.
  I wondered about these being Experimental or Internal instead.

Author: epage

README.md

@@ -9,17 +9,19 @@ Cargo downloads your Rust project’s dependencies and compiles your project.
 [The Cargo Book]: https://doc.rust-lang.org/cargo/
 [Cargo Contributor Guide]: https://rust-lang.github.io/cargo/contrib/
 
+> The Cargo binary distributed through with Rust is maintained by the Cargo
+> team for use by the wider ecosystem.
+> For all other uses of this crate (as a binary or library) this is maintained
+> by the Cargo team, primarily for use by Cargo and not intended for external
+> use (except as a transitive dependency). This crate may make major changes to
+> its APIs.
+
 ## Code Status
 
 [![CI](https://github.com/rust-lang/cargo/actions/workflows/main.yml/badge.svg?branch=auto-cargo)](https://github.com/rust-lang/cargo/actions/workflows/main.yml)
 
 Code documentation: <https://doc.rust-lang.org/nightly/nightly-rustc/cargo/>
 
-## Installing Cargo
-
-Cargo is distributed by default with Rust, so if you've got `rustc` installed
-locally you probably also have `cargo` installed locally.
-
 ## Compiling from Source
 
 ### Requirements

benches/benchsuite/README.md

@@ -0,0 +1,3 @@
+> This crate is maintained by the Cargo team, primarily for use by Cargo
+> and not intended for external use. This
+> crate may make major changes to its APIs or be deprecated without warning.

benches/benchsuite/src/lib.rs

@@ -1,3 +1,7 @@
+//! > This crate is maintained by the Cargo team, primarily for use by Cargo
+//! > and not intended for external use. This
+//! > crate may make major changes to its APIs or be deprecated without warning.
+
 #![allow(clippy::disallowed_methods)]
 
 use cargo::GlobalContext;

crates/cargo-platform/README.md

@@ -0,0 +1,2 @@
+> This crate is maintained by the Cargo team for use by the wider
+> ecosystem. This crate follows semver compatibility for its APIs.

crates/cargo-platform/src/lib.rs

@@ -6,6 +6,9 @@
 //!
 //! See `examples/matches.rs` for an example of how to match against a `Platform`.
 //!
+//! > This crate is maintained by the Cargo team for use by the wider
+//! > ecosystem. This crate follows semver compatibility for its APIs.
+//!
 //! [`Platform`]: enum.Platform.html
 
 use std::fmt;

crates/cargo-test-macro/README.md

@@ -1,5 +1,3 @@
-WARNING: You might not want to use this outside of Cargo.
-
-* This is designed for testing Cargo itself. Use at your own risk.
-* No guarantee on any stability across versions.
-* No feature request would be accepted unless proved useful for testing Cargo.
+> This crate is maintained by the Cargo team, primarily for use by Cargo
+> and not intended for external use. This
+> crate may make major changes to its APIs or be deprecated without warning.

crates/cargo-test-macro/src/lib.rs

@@ -3,11 +3,9 @@
 //! This is meant to be consumed alongside `cargo-test-support`. See
 //! <https://rust-lang.github.io/cargo/contrib/> for a guide on writing tests.
 //!
-//! WARNING: You might not want to use this outside of Cargo.
-//!
-//! * This is designed for testing Cargo itself. Use at your own risk.
-//! * No guarantee on any stability across versions.
-//! * No feature request would be accepted unless proved useful for testing Cargo.
+//! > This crate is maintained by the Cargo team, primarily for use by Cargo
+//! > and not intended for external use. This
+//! > crate may make major changes to its APIs or be deprecated without warning.
 
 use proc_macro::*;
 use std::path::Path;

crates/cargo-test-support/README.md

@@ -1,5 +1,3 @@
-WARNING: You might not want to use this outside of Cargo.
-
-* This is designed for testing Cargo itself. Use at your own risk.
-* No guarantee on any stability across versions.
-* No feature request would be accepted unless proved useful for testing Cargo.
+> This crate is maintained by the Cargo team, primarily for use by Cargo
+> and not intended for external use. This
+> crate may make major changes to its APIs or be deprecated without warning.

crates/cargo-test-support/src/lib.rs

@@ -11,11 +11,9 @@
 //!   targeted at cargo contributors
 //!   - Updated on each update of the `cargo` submodule in `rust-lang/rust`
 //!
-//! **WARNING:** You might not want to use this outside of Cargo.
-//!
-//! * This is designed for testing Cargo itself. Use at your own risk.
-//! * No guarantee on any stability across versions.
-//! * No feature request would be accepted unless proved useful for testing Cargo.
+//! > This crate is maintained by the Cargo team, primarily for use by Cargo
+//! > and not intended for external use. This
+//! > crate may make major changes to its APIs or be deprecated without warning.
 //!
 //! # Example
 //!

crates/cargo-util-schemas/README.md

@@ -0,0 +1,2 @@
+> This crate is maintained by the Cargo team for use by the wider
+> ecosystem. This crate follows semver compatibility for its APIs.