Add README section on general usage

docs/README

@@ -0,0 +1,38 @@
+# General Usage
+
+## Prerequisites
+
+  You must have avr-gcc and avrdude installed. To install it
+  on a debian-based system, please run the following command:
+
+        apt install avr-gcc avrdude
+
+## Build and Flash
+
+  Run this next command in the project root directory to
+  build and flash the project using an usbasp programmer:
+
+        make all
+
+  See the Makefile for different settings for your specific
+  build environment. To remove all build related files you
+  may run this command:
+
+        make clean
+
+## Setting Temperature and Dewpoint Targets
+
+  You can use the script below to send serial commands (you
+  may need to run 'git submodule update --init' if the tools
+  directory is empty):
+
+        ./opt/tools/serial-send.py <command> <args ...>
+
+  Issue the SET command to update the target settings:
+
+        SET <temperature> <dewpoint>
+
+  Settings are stored in EEPROM and are persistent until a new
+  SET command is issued. Keywords are not case-sensitive. Both
+  arguments may contain a decimal point followed by a sequence
+  of digits.