Update README.md.

Author: python-processing-unit

README.md

@@ -1,3 +1,69 @@
-This is the canonical implementation of the Prefix programming language in C17, targeting Clang on baseline x64 Windows.
+# Prefix
 
-The versioning system used is [SemVer 2.0](https://semver.org/).
+C17 implementation of the Prefix programming language.
+
+Overview
+--------
+
+This repository contains the reference implementation of the Prefix
+programming language, written in ISO C17 and targeting Clang on baseline
+ x64 Windows. The codebase includes the lexer, parser, interpreter\runtime,
+standard library bindings, and supporting tools used by the reference
+implementation.
+
+Project layout
+--------------
+
+- `.github\workflows\`: GH Actions CI configuration.
+- `docs\`: Documentation for Prefix, builds GH Pages site.
+- `ext\`
+- `lib\`
+- `src\`: Source code and headers for the interpreter.
+- `tests\`: Automated test suite.
+- `.gitignore`: Git ignore file.
+- `build.ps1`: Build script for the interpreter and tests.
+- `README.md`: This file.
+
+
+Requirements
+-------------
+
+- Windows Vista or newer.
+- LLVM\Clang toolchain with C17 support.
+- PowerShell (to run the included build script)
+
+Building
+--------
+
+To build the interpreter run:
+
+```powershell
+& path\to\Prefix\build.ps1
+```
+
+The `build.ps1` script invokes Clang and produces the interpreter, standard library, and test binaries.
+Ensure your Clang installation is on `PATH` before running the script.
+
+Testing
+-------
+
+Automated tests live under the top-level `tests\` directory. You can run the test harness with PowerShell:
+
+```powershell
+& path\to\Prefix\tests\test.ps1
+```
+
+Documentation
+-------------
+
+The docs are located in `Prefix\docs\`.
+
+License
+-------
+
+Prefix is distributed under the [Unlicense](https://unlicense.org/).
+
+Versioning
+----------
+
+Prefix follows [SemVer 2.0](https:\\semver.org), treating [the specification](https://python-processing-unit.github.io/Prefix/SPECIFICATION.html) as the public API.