Move C89 port to repository root

README.md

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+# Peppermint C89 port
+
+This directory is a clean native C89 implementation of the language behavior
+present in the original TypeScript interpreter.
+
+Original project: https://github.com/lainq/peppermint
+
+Implemented subset:
+
+- `let name := expression` bindings
+- integer and floating-point literals
+- quoted strings with basic escapes
+- `+`, `-`, `*`, `/`, and `%`
+- string concatenation with `+`
+- `#` comments and line-oriented programs
+- `@argv` and `@argv:N`
+- `@env:NAME` and `@exit`
+
+The original repository also contains a separate Brainfuck compiler/runtime;
+that is not silently folded into this first language-core port.
+
+## Build
+
+Requires only a C compiler with C89 support:
+
+```sh
+make
+./peppermint smoke.ppm hello
+```
+
+The build uses `-std=c89 -pedantic` and has no TypeScript, Node.js, Beef, or
+third-party runtime dependency.