Add README with specs

README.md

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+# Ultimate ECP5 Board
+
+## Key Features
+ - Largest ECP5; LFE5UM5G-85F
+ - PCIe 2.0 x2 card edge connector on two SERDES channels
+ - Remaining two SERDES channels muxed using high-speed mux:
+   - 2-lane mini DisplayPort transmit and receive connectors
+   - or USB type-C connector (with proper CC logic and ULPI PHY for USB 2.0)
+   - Must have flexible SERDES clocking for a range of protocols with passive adapters (SFP, SATA, etc) 
+ - 1GByte or 2GByte x32 DDR3, either chips or half SODIMM
+ - Dedicated HDMI output, probably using TFP410 serialiser for a simpler video output than DP
+ - Dual GbE connectors with RGMII PHYs
+ - USB-A 2.0 host connector with ULPI PHY
+ - 2nd USB-A connector directly connected to FPGA
+ - FT2232H for debug JTAG and UART/FIFO on second USB type-C connector also used for normal board power (up to 5V 3A)
+ - Optional PCIe 12V power input connector
+ - At least 8 user LEDs, 4 user buttons, 4 or 8 user DIP switches
+ - 128Mbit QSPI flash for boot and data
+ - microSD card connector
+ - Audio I/O with I2S codec
+ - Dual PMOD connector
+ - As many remaining IO as possible on high speed FFC connectors with a differential optimised pinout (at least 100-150 IO using this)
+
+## Layout
+ - PCIe card form factor
+ - At least Ethernet, 2x miniDP and 2x USB-C on exposed side when in a case used as a PCIe card 
+ - Other connectors probably would have to be on other sides. FFC connectors probably on top so they can loop over to another card to form a 2-slot card (e.g. with ADCs/DACs for SDR/DAQ)
+
+## Possible accessories using high-speed FFC connectors
+ - MIPI DSI smartphone-style LCDs
+ - MIPI CSI-2 cameras
+ - High speed ADC/DAC
+ - HDMI in/out, direct or using serialiser chip
+ - LVDS video in/out for LCDs or block cameras
+ - Breakout board to dual or triple PMOD