Doc: Add reference to architecture in README

README.md

@@ -5,6 +5,7 @@ The system contain a number of peripherals (I2C, SPI, GPIO, PWM, UART, and DMA)
 It is designed for use on FPGA and specifically targets the [Sonata FPGA board](./doc/architecture/board.md).
 
 It is under active development and the first full RTL release is not yet complete.
+In the meantime, please read the [architecture specfication](./doc/architecture/intro.md).
 
 Sonata is part of the [Sunburst Project](https://www.sunburst-project.org) funded by [UKRI](https://www.ukri.org/) / [DSbD](https://www.dsbd.tech/).