Doc: Add README for the ROM core.

Signed-off-by: Joachim Strömbergson <[email protected]>

hw/application_fpga/core/rom/README.md

@@ -0,0 +1,20 @@
+# rom
+ROM for the firmware (FW).
+
+
+## Introduction
+This core implements the ROM where the FW is stored.
+
+
+## API
+The core does not have an API.
+
+
+## Implementation Details
+The core is implemented by implicitly allocating a number of Embedded
+Block Memory (EBM) cores, also known as SB_RAM40_4K.
+
+During building of the FPGA bitstream the ROM binary image is mapped
+into the ROM address space. When the FPGA is configured by the
+bitstream, the SB_RAM40_4K cores are loaded with the ROM. The contents
+is not changed by a system reset.