Add additional collected wisdom to README.md.

README.md

@@ -14,4 +14,35 @@ Tool and library for flashing their RISC-V MCUs.
 
 - [ ] Another code style
 - [ ] Finalize API
-- [ ] SDIO and JTAG support
+- [ ] SDIO and JTAG support
+
+# Build
+
+This project is not self-contained. After you check out the master project
+from GitHub, you must fetch the additional vendor libraries via:
+$ git submodule update --init --recursive
+
+If vendor/argtable3 and vendor/libserialport/ are empty, this step has
+failed and should be investigated.
+
+# Usage
+
+  blisp write -c <chip_type> [-p <port_name>] <input>
+  blisp [--help] [--version]
+
+A typical invocation may therefore be:
+
+  blisp write -c bl70x -p /dev/tty.usbmodem0000000200001
+
+If you wish to see a painful level of debugging, set the environmental
+variable LIBSERIALPORT_DEBUG before running. You can either export this
+in your shell or change it for a single run via
+
+  LIBSERIALPORT_DEBUG=y ./a.out write -c bl70x -p /dev/tty.usbmodem0000000200001
+
+Because this is done at the lowest level of serial communication, the
+displays aren't packet-aware or know about the chip's command set or such.
+This is really only useful for debugging systems-level issues withing
+the device or blisp itself.
+
+