init

First attempt at both Rust and snix-castore.
I'll start by putting together a single-file CLI app,
no splitting modules out until needed, no separation of concerns.

Currently, just the fetching is implemented:

```
$ sidx pkgs/dev*/cuda-*/cuda/manifests/*.json
```

README.md

@@ -0,0 +1,20 @@
+sidx
+===
+
+
+Indexing archives and build outputs.
+
+
+Roadmap
+---
+
+
+- [x] PoC: basic `reqwest` fetcher, minimal `snix-castore` integration, claims of the form "`$uri` referred to `$blake3` at `$time`" stored in sqlite.
+- [ ] Zip, tar, git fetchers.
+- [ ] ELF scanning: claims of the form "`$blake3` is ELF" and "$blake3's `DT_RUNPATH` is `$runpath`", etc. (`DT_NEEDED`, `.interp`, symbols exported in `.data` and `.text`)
+- [ ] `cuobjdump` scanner: claims of the form "$blake3 contains `PTX` or `SASS` code for $gencode".
+
+Approach
+---
+
+Vapourware and means to an end.