Restore SW:Linux:X11 page from the wiki history

This reverts commit fff622c.

Author: davide125

docs/SW-Linux-X11.md

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+# Running X11
+ * You can run a non-accelerated X11 if you build the kernel with
+`CONFIG_DRM_FBDEV_EMULATION=y`
+ * After booting that kernel install the relevant xserver fbdev (under debian)
+`sudo apt install xserver-xorg-video-fbdev`
+ * Then you can try starting X
+`startx`
+ * If you have problems look for error messages in the Xserver log 
+`less /var/log/Xorg.0.log`
+ * Assuming you get X starting up then will need to set up a window manager - as per your distribution e.g. see this Debian [GUI system](https://www.debian.org/doc/manuals/debian-reference/ch07.en.html)
+ * I installed the very light keyboard based fluxbox
+`apt install fluxbox`
+ * To get a simple graphical login screen
+`apt install xdm`
+ * I install the nice X terminal **konsole**
+`apt install konsole`
+ * For a web browser install firefox as Chrome requires special kernel paging support (not available at this time)
+`sudo apt install firefox-esr`
+
+(![X11 running on Macbook Air 2020](https://raw.githubusercontent.com/amworsley/asahi-wiki/main/images/mba-xorg-fbdev.png))