added very brief descriptions of the PCB design and calibration software

README.md

@@ -30,8 +30,9 @@ The 3D models currently include the TinySpHEAR, a four capsule first order Ambis
 
 ## Electronics
 
-Watch this space for Kicad circuit description and printed circuit board designs of the simple Zapnspark interface circuit
+The pcb/zapnspark directory contains the Kicad electrical circuit and printed circuit board design for the Zapnspark phantom power interface. The current printed circuit board design fits into four slots carved inside the body of the [TinySpHEAR plus Zapnspark model](doc/TinySpHEAR_zapnspark.md). Everything is dimensioned for the sizes of the components specified in the parts list, any changes (specially the diameter of the electrolytic capacitors) would need to be taken into account by changing appropriate model parameters. 
 
 ## Calibration
 
-Watch this space for Octave calibration code
+The calibration/src directory contains the Octave files for the current calibration software. The CALIBRATION.md file in there has a very brief description of usage, but currently is out of date with the current source code. Look into the individual files for more guidance. Hopefully this will be fixed soon.
+