Docs add kernel build instructions

docs/building_kernel.md

@@ -0,0 +1,44 @@
+# Building the MOP3 kernel
+
+This article describes, how to build the kernel, how the build system works and prerequisites.
+
+## Preprequistes
+
+- POSIX host system (tested on Linux, may break on other systems)
+- Git
+- GNU make
+- LLVM toolchain/Clang C compiler
+- Xorriso
+
+## Build steps
+
+cd into root of MOP3 source tree.
+
+Build the kernel:
+```
+make -B all_kernel buildtype=<debug|release>
+```
+
+Build essential system applications:
+```
+make -B all_apps
+```
+
+Prepare the ramdisk:
+```
+make -B all_dist
+```
+
+Build ISO image:
+```
+./aux/limine_iso_amd64.sh
+```
+
+Now you have an ISO image, which can be run my QEMU or you can burn it onto a CD.
+
+For the convenience of the developer, there's a magic "do all" script located in `aux`:
+```
+./aux/devel.sh # optionally "./aux/devel.sh debug" for debugging
+```
+
+It does all the previous steps, just packed into a single script.