docs: add readme, images

README.md

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+# Lock Puzzle
+
+A 3D-printed puzzle box written in OpenSCAD.
+
+![The puzzle box in its closed state](images/lockpuzzle_rendered_locked.png)
+
+![The puzzle box in its opened state](images/lockpuzzle_rendered_unlocked.png)
+
+## Usage
+
+### Rendering
+
+1. Make sure you have OpenSCAD installed.
+2. In the file `render.sh`, change at least the `LENGTH` variable to the length of your chosen password.
+    - You can also change other settings such as the alphabet, or the diameter of the box.
+	- The default diameter (and the one the printed model has been tested with) is 50mm.  The lock mechanism takes 20mm off this, so the inner diameter is 30mm.
+	- The length of the box currently depends on the length of the password, and is `(LENGTH*10+15)mm`.  The length of the inner space is `(LENGTH*10)mm`.
+3. Run `./render.sh`, which will create all the STL files you'll need in the `out/` directory.
+    - If you are using an OpenSCAD version without support for the Manifold rendering engine, remove the `--backend=manifold` argument.
+
+### 3D Printing
+
+Print the following objects:
+
+- 1 x `case.stl`
+- 1 x `plug.stl`
+- 1 x `key_dial_${character}.stl` for every character in your password.
+- LENGTH x `ring_click.stl`
+- 1 x `ring.stl`
+
+### Assembly
+
+1. Start with the printed case:
+
+    ![Rendering of the main case of the lock](images/lockpuzzle_assembly_01.png)
+2. Add the first ring to the case as shown here.  Note that the outward-pointing position indicator and the sideways-pointing "clicker" must be oriented exactly as shown here:
+
+    ![The first ring placed on the case](images/lockpuzzle_assembly_02.png)
+3. Add the first dial case as shown here.
+
+    ![The first dial placed on the case](images/lockpuzzle_assembly_03.png)
+4. Repeat steps 2 and 3 until you reach the last dial.
+
+    ![The remaining rings and dials placed on the case](images/lockpuzzle_assembly_04.png)
+5. Add the final ring to the case as shown here.  Note the absence of the clicker.
+
+    ![The final ring placed on the case](images/lockpuzzle_assembly_05.png)
+6. Turn all dials so that the cutout lines up with the long slot in the case.  Turning the dials might require quite some force at first, but after a few turns the clicker will wear down a bit, which will make the dials easier to turn.
+
+    ![All dials lined up with the slot in the case](images/lockpuzzle_assembly_06.png)
+7. Finally, insert the plug all the way, then turn the dials to lock the puzzle box:
+
+    ![The plug inserted into the case, closing the puzzle box](images/lockpuzzle_assembly_07.png)