Add README and license

LICENSE

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+Customizable Card Dividers © 2025 by crater2150 is licensed under Creative Commons Attribution-ShareAlike 4.0 International
+See https://creativecommons.org/licenses/by-sa/4.0/

README.md

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+# Customizable dividers for your card games (or other cards)
+
+With this OpenSCAD script, you can create tabbed dividers with custom icons for
+any card size. It started out as a way to automate adding more expansions to my
+Arkham Horror dividers, now it is flexible enough to be used for any type of cards.
+
+## Parameters for Customizing
+
+*Card dimensions:* The most important parameters are `horizontal` and `vertical`. Set these to the
+size of your cards. The longer side should be assigned to `horizontal` for
+sideways storage, or to `vertical` for upright storage.
+
+*Tabs:* Depending on the size set for `horizontal`, the number and size of tabs must be
+configured:
+
+- `tab_width` is the length of the top edge
+- `tab_height` is the distance between the tab's top edge and the cards' top edge
+- `tab_angle` sets the slope in degrees. Higher numbers mean wider slope. With 45 degrees, the slope will be as wide as tall, i.e.
+- `tab_height`. With 0 degrees, there will be no slope.
+- `tabs` sets the total number of tabs along the top edge. They will be spaced evenly, with the outer tabs only having a slope on the inner side.
+- `index` sets the tab index for the current card. The index 0 will be the leftmost tab. Some recommended settings, based on Arkham Horror cards:
+
+|--------------------------------------------------------|
+| horizontal | tabs | tab_width | tab_angle | tab_height |
+|------------|------|-----------|-----------|------------|
+| 87         | 4    | 16        | 45        | 10         |
+| 61         | 3    | 14        | 30        | 10         |
+|------------|------|-----------|-----------|------------|
+
+To try out other values, you can set `test_tabs` to true. This will ignore the
+`index` setting and render as many dividers as there are tabs, put above each
+other, so you can see how much the tabs overlap.
+
+*Icons:* Set `icon` to the path to an SVG file (or upload one if using the web
+interface). The icon will be scaled down to have a height of
+`target_icon_height`. You can additionally set the `target_icon_width`. If you
+leave that at 0, the icon will keep it's aspect ratio, which will cause it to be
+off center, if it isn't square. Also, if it is much wider than tall, it can
+cause it to spill over.