Clarify which org maintains riscv-rust-quickstart

[9names]

According to the landing page of the wg repo:

### The RISC-V team

The RISC-V team develops and maintains the core of the RISC-V crate ecosystem.

#### Members

- [@almindor]
- [@dkhayes117]
- [@romancardenas]
- [@MabezDev]
- [@jessebraham]
- [@rmsyn]

#### Projects

Projects maintained by this team

- [`riscv-rust-quickstart`]
- [`riscv-pac`]
- [`riscv-rt`]
- [`riscv-semihosting`]
- [`riscv`]

According to https://github.com/riscv-rust/teams

The e310x team

Maintains all the crates related to E310x chips.
Members

    [@romancardenas](https://github.com/romancardenas)

Projects

Projects maintained by this team.

    [e310x](https://github.com/riscv-rust/e310x)
    [riscv-rust-quickstart](https://github.com/riscv-rust/riscv-rust-quickstart)

Related issues:
#866
riscv-rust/teams#1

[romancardenas]

If we want the WG to maintain (something like) riscv-rust-quickstart, then we must consider including this crate inside the riscv workspace and removing it from an external organization.

In any case, the current riscv-rust-quickstart is quite outdated and needs some work. I will try to address this as soon as possible.