Add Readme

Readme.md

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+# A raspberry 3 OS
+
+Support:
+1. UART
+2. Framebuffer
+3. update over serial
+4. Qemu
+
+## UART
+Using GPIO 14 and 15
+
+## update over serial
+
+You can update a kernel that is connected a given TTY with
+`TTY=/dev/MYTTY make update_serial`
+
+This is mainly usefull for kernel running on a real board but to use it with QEMU, you have to modify the serial opt to be
+`-serial pty`
+
+and then
+`TTY=/TTY_VERBOSED_BY_QEMU make update_serial`
+
+## QEMU
+
+You can test it with
+` make run`
+
+### Qemu with a debugger
+
+`make debug`
+
+# Install on sdcard
+
+Create a FAT32 partion and copy kernel and kernel8.img