Add x1 experiments

x1/README.md

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+#### Code
+ - `mrc.S`  Read SCTLR (MMU etc.) and return
+ - `return.S`  Return immediately
+ - `extract.py`  Extract .text
+
+
+#### Build
+```sh
+pip3 install pyelftools
+make all
+```
+
+#### Run
+ - Create a directory `/path/to/sd/APP/foo`
+ - Create index.din `touch /path/to/sd/APP/foo/index.din`
+ - Copy and rename the raw executable `cp foo.bin /path/to/sd/APP/foo/AppMain.bin`