feat: add basic tag holder (#266)

Includes CAD source so modifications should be easy.

Hardware/M3 2.2 Newton mounting plate by kquinsland/readme.md

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+<!-- markdownlint-disable-file MD045 -->
+# Mounting plate for the M3 2.2 Newton board
+
+This is a super basic / minimal mounting plate for the M3 2.2 Newton ESLs.
+
+![Render of the mount](tag-in-mount.png)
+
+The geometry is similar on the rest of the M3 family so using this with the other sizes should be as simple as scaling in your slicer but I don't have any of the other sizes to verify this.
+
+The[`flat-surface-mount.step`](./flat-surface-mount.step) file is provided for easy adjustment in your CAD package of choice or - if your slicer [supports it](https://blog.prusa3d.com/prusaslicer-2-5-is-here-new-perimeter-generator-step-file-support-lightning-infill-and-more_70562/) - direct printing.
+
+I have also included the [f360 archive](./flat-surface-mount.f3z) so you can modify as needed.
+It references / uses the [`M3_2.2-inch_esl-module.f3d`](OpenEPaperLink/Hardware/M3 2.2 Newton Jig by kquinsland/M3_2.2-inch_esl-module.f3d) file as well.
+
+All files are licensed under the [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/) license.
+
+## Printing
+
+The suggested print orientation is shown below:
+
+![Print orientation](./print-orientation.png)
+
+No support material is needed.
+Print in any material you like but I used PLA because it's what I had on hand.
+There are a few small features so relatively thin layer height and a small nozzle are recommended.
+I have gotten acceptable results with a `0.4` mm and `0.6` mm nozzle and `0.2`mm layer height but your mileage may vary.
+
+## Assembly
+
+The mount features a shallow recess on the back that is just wide enough for a small 3M Command Strip to fit.
+You can also use double-sided tape or glue if you prefer.
+
+![set of components](set.jpg)
+
+There's only one way that the tag fits into the mount:
+
+![tag in mount](./eject-slot-demo.jpg)
+
+The mount was designed to be a tight snap fit so the tag could safely be mounted to appliances that vibrate or moved around a lot.
+If you need to remove the tag for any reason, you should use a small flat head screwdriver or similar to gently pry the tag out of the mount.
+
+Counter intuitively, the best place to pry from is **not** the place that looks like it'll be the best place to pry from.
+You'll have an easier time prying from the side pictured above.