util: Add description.md to each util

Descriptions are taken from the files themselves or READMEs. Description
followed by a space with the language in marked up as code.

Change-Id: I5f91e85d1034736289aedf27de00df00db3ff19c
Signed-off-by: Tom Hiller <thrilleratplay@gmail.com>
Reviewed-on: https://review.coreboot.org/27563
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/riscv/description.md

@@ -0,0 +1,6 @@
+__riscv__
+  * _make-spike-elf.sh_ - Converts a flat file into an ELF, that can be
+                          passed to SPIKE, the RISC-V reference
+                          emulator.`Bash`
+  * _sifive-gpt.py_ - Wraps the bootblock in a GPT partition for
+                      SiFive's bootrom. `Python3`