Add readme

Author: sergv

Readme.md

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+[![build](https://github.com/pointfree-wasm/pointfree-wasm.github.io/actions/workflows/ci.yml/badge.svg)](https://github.com/pointfree-wasm/pointfree-wasm.github.io/actions/workflows/ci.yml)
+
+# Synopsis
+
+This is a pretty simple Haskell application that runs entirely in the browser thanks to Web Assembly.
+
+The idea was to try out how WASM Haskell backend would handle a package with non-trivial functionality but complicated user interface. The (pointfree package)[https://hackage.haskell.org/package/pointfree] was great fit since it does interesting transformation while its interface is just a string from a user for input and a list of strings for output.
+
+Apart from working pointfree converter in a browser this project might be interesting as a working example on how to use Haskell WASM backend to make other browser applications.
+
+# Building and running locally
+
+These steps are made for Linux/MacOS but should work on Windows as well potentially with some tweaking.
+
+If in doubt you can check how this project’s CI is set up and copy steps from there: https://github.com/pointfree-wasm/pointfree-wasm.github.io/blob/master/.github/workflows/ci.yml. The advantage of CI is that it’s a working version.
+
+## Step 0 - get ordinary Haskell development up and running
+
+Install `ghc` and `cabal`. A good way to do so is via (`ghcup`)[https://www.haskell.org/ghcup/].
+
+## Step 1 - obtaining GHC WASM backend
+
+Please refer to https://gitlab.haskell.org/ghc/ghc-wasm-meta for detailed instructions.
+
+For example, if you use `nix` package manager then use following flake-based command:
+
+```
+$ nix shell https://gitlab.haskell.org/ghc/ghc-wasm-meta/-/archive/master/ghc-wasm-meta-master.tar.gz
+```
+
+## Step 2 - ensure `happy` executable is in your PATH
+
+Optionally do `cabal update`, then execute `cabal install happy` with regular ghc.
+
+If you haven’t done so, add cabal’s installation directory to PATH:
+
+```
+$ export PATH="$HOME/.cabal/bin:$PATH"
+```
+
+Check with `happy --version` that executable is available in the PATH environment variable:
+
+```
+$ happy --version
+Happy Version 1.20.1.1 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow
+
+Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY.
+This program is free software; you can redistribute it and/or modify
+it under the terms given in the file 'LICENSE' distributed with
+the Happy sources.
+```
+
+NB this step is needed because `haskell-src-exts` depends on the `happy` build tool but `haskell-src-exts` wasn’t updated to let `cabal` quietly provide `happy` during build so `happy` executable has to be on the PATH for the time being.
+
+## Step 3 - build WASM file and other dependencies
+
+After `wasm32-wasi-cabal build all` the resulting `.wasm` file will be at path returned by `wasm32-wasi-cabal list-bin pointfree-wasm:exe:pointfree-wasm`. Link it to the directory where `index.html` is located, i.e. the project’s root.
+
+```
+$ ln -s $(wasm32-wasi-cabal list-bin pointfree-wasm:exe:pointfree-wasm) .
+```
+
+Then generate `pointfree-wasm.js`:
+
+```
+$ $(wasm32-wasi-ghc --print-libdir)/post-link.mjs -i $(wasm32-wasi-cabal list-bin pointfree-wasm:exe:pointfree-wasm) -o pointfree-wasm.js
+```
+
+## Step 4 - run web server in project’s root
+
+Any web server would do, good starting point is `python3 -m http.server` if Python is installed.
+
+Now you can open the address the web server is running on in the browser and it should work.