added a document on building PsychOS. Work in progress.

docs/building.md

@@ -0,0 +1,15 @@
+# Building PsychOS
+## Building
+```
+./genkernel.sh
+```
+Builds a kernel using files in `build.cfg` and saves it to `kernel.lua`
+## Files
+### genkernel.sh
+genkernel.sh calls `genkernel.lua build.cfg`.
+### genkernel.lua
+Wrapper for modules/applications/genkernel.lua. Runs it with arguments.
+### modules/applications/genkernel.lua
+Both a PsychOS module and usable as a program.
+#### genkernel(*bp*, *kn*)
+Builds a kernel using the modules listed in *bp*, with \_OSNAME including *kn*.