Add RISC-V boards (#168)

Add SiFive and RISC-V crates.

Author: vmedea

README.md

@@ -123,6 +123,10 @@ Peripheral Access Crates were also called Device Crates.
 - [`mkw41z`](https://crates.io/crates/mkw41z) - ![crates.io](https://img.shields.io/crates/v/mkw41z.svg)
 - [`k64`](https://crates.io/crates/k64) - ![crates.io](https://img.shields.io/crates/v/k64.svg)
 
+### SiFive
+
+- [`e310x`](https://github.com/riscv-rust/e310x) - svd2rust generated interface to SiFive [Freedom E310](https://www.sifive.com/cores/e31) MCUs - ![crates.io](https://img.shields.io/crates/v/e310x.svg)
+
 ### STMicroelectronics
 
 - [`stm32f103xx`](https://crates.io/crates/stm32f103xx) Peripheral access API for STM32F103XX microcontrollers (generated using svd2rust) - ![crates.io](https://img.shields.io/crates/v/stm32f103xx.svg)
@@ -179,6 +183,10 @@ Also check the list of [NXP board support crates][nxp-bsc]!
 
 - [`mkw41z-hal`](https://crates.io/crates/mkw41z-hal) - ![crates.io](https://img.shields.io/crates/v/mkw41z-hal.svg)
 
+### SiFive
+
+- [`e310x-hal`](https://github.com/riscv-rust/e310x-hal) - HAL for SiFive [Freedom E310](https://www.sifive.com/cores/e31) MCUs - ![crates.io](https://img.shields.io/crates/v/e310x-hal.svg)
+
 ### STMicroelectronics
 
 Also check the list of [STMicroelectronics board support crates][stm-bsc]!
@@ -239,6 +247,10 @@ Crates tailored for general CPU architectures.
 - [`cortex-m`](https://github.com/japaric/cortex-m) Low level access to Cortex-M processors - ![crates.io](https://img.shields.io/crates/v/cortex-m.svg)
 - [`cortex-a`](https://github.com/andre-richter/cortex-a) Low level access to Cortex-A processors (early state) - ![crates.io](https://img.shields.io/crates/v/cortex-a.svg)
 
+### RISC-V
+
+- [`riscv`](https://github.com/rust-embedded/riscv) Low level access to RISC-V processors - ![crates.io](https://img.shields.io/crates/v/riscv.svg)
+
 ## Board support crates
 
 Crates tailored for specific boards.
@@ -261,6 +273,10 @@ Crates tailored for specific boards.
 
 [FRDM-KW41Z]: https://www.nxp.com/products/processors-and-microcontrollers/arm-based-processors-and-mcus/kinetis-cortex-m-mcus/w-serieswireless-conn.m0-plus-m4/freedom-development-kit-for-kinetis-kw41z-31z-21z-mcus:FRDM-KW41Z
 
+### SiFive
+
+- [`hifive1`](https://github.com/riscv-rust/hifive1) - Board support crate for [HiFive1](https://www.sifive.com/boards/hifive1) and [LoFive](https://hackaday.io/project/26909-lofive) boards - ![crates.io](https://img.shields.io/crates/v/hifive.svg)
+
 ### Sony
 
 - [`prussia`](https://github.com/ZirconiumX/prussia) - SDK for the PlayStation 2.