prototype: init directory with nixdoc outline

prototypes/README.md

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+# prototypes
+
+Sometimes I have an idea for something, but it's very much not fleshed
+out, and so... I start with `cargo new <name>`, and start coding.
+Sometimes these are just design documents, and sometimes they are
+half-functional tools.
+
+This directory is meant for me, or you if you are curious about the
+way I think, and approach problems.  None of these tools are really
+working, or else they would be in the `apps/` or `development/` trees
+😉 - so be warned.

prototypes/nixdoc/Cargo.toml

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+[package]
+name = "nixdoc"
+version = "0.1.0"
+authors = ["Mx Kookie <kookie@spacekookie.de>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

prototypes/nixdoc/README.md

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+# nixdoc
+
+Imagine rustdoc, but for nix.
+
+
+* Parse `.nix` files
+* Generate documentation, based on outputs
+* Modules are already documented in nixos options
+  * What could this do better?  Better browsability?  Maybe just a
+    different front-end for the existing parsing mechanism?
+* Parsing comments, and associating them with entries?
+* Document function inputs/ outputs
+* 

prototypes/nixdoc/src/main.rs

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+fn main() {
+    println!("Hello, world!");
+}