added readme

tests/test-files/unsupported/README.md

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+# Unsupported Files
+
+Files containing unsupported gcodes
+
+We can however still deal with these, workarounds shown below
+
+## Unsupported GCodes
+
+
+When attempting to process unsupported gcode(s) via a `Machine` the following error (or similar) will be raised
+
+    MachineInvalidState: unsupported gcode(s): 'P1 M10' (machine mode: <Mode: G00 G17 G90 G90.1 G94 G21 G40 G49 G54 G61 G97 M05 M09 F600 S0 T0>)
+
+
+These codes are not currently supported by this library, but you may introduce
+them for your project. with the following workaround
+
+**Workaround**
+
+Any class inheriting `GCode` is used to parse each gcode string.
+
+Look to the root `GCode` class definition in `gcodes.py` for more details.
+
+So, create the following class(es) (anywhere in your codebase, as long as it's
+imported)
+
+
+### `M10` / `M11` : Pallet Clamp
+
+    import pygcode
+
+    class GCodePalletClampOn(pygcode.GCode):
+        """M10: Pallet clamp on"""
+        word_key = pygcode.Word('M', 10)
+        word_letter = 'M'
+        param_letters = set('P')
+
+    class GCodePalletClampOff(pygcode.GCode):
+        """M10: Pallet clamp off"""
+        word_key = pygcode.Word('M', 11)
+        word_letter = 'M'
+        param_letters = set('P')
+
+
+### `G70` / `G71` : Fixed cycle, multiple repetitive cycle
+
+    import pygcode
+
+    class GCodeFixedCycleMultiRepCycleRough(pygcode.GCode):
+        """G70: Fixed cycle, multiple repetitive cycle, for finishing (including contours)"""
+        word_key = pygcode.Word('G', 70)
+        word_letter = 'G'
+
+    class GCodeFixedCycleMultiRepCycleRough(pygcode.GCode):
+        """G71: Fixed cycle, multiple repetitive cycle, for roughing (Z-axis emphasis)"""
+        word_key = pygcode.Word('G', 71)
+        word_letter = 'G'