Add missing links from README.md to new spi examples (#214)

Author: kilograham

README.md

@@ -162,6 +162,8 @@ App|Description
 [spi_dma](spi/spi_dma) | Use DMA to transfer data both to and from the SPI simultaneously. The SPI is configured for loopback.
 [spi_flash](spi/spi_flash) | Erase, program and read a serial flash device attached to one of the SPI controllers.
 [spi_master_slave](spi/spi_master_slave) | Demonstrate SPI communication as master and slave.
+[max7219_8x7seg_spi](spi/max7219_8x7seg_spi) | Attaching a Max7219 driving an 8 digit 7 segment display via SPI
+[max7219_32x8_spi](spi/max7219_32x8_spi) | Attaching a Max7219 driving an 32x8 LED display via SPI
 
 ### System