added readme

Author: iliabylich

README.md

@@ -0,0 +1,95 @@
+# Node.js bindings for `lib-ruby-parser`
+
+It's based on [C++ bindings](https://github.com/lib-ruby-parser/cpp-bindings) and `node-addon-api`.
+
+Each node has its own JavaScript class, so
+1. it's possible to dinstinguish them by checking `instanceof`
+2. they can be extended in pure JavaScript
+
+Here's how it looks like:
+
+```js
+ParserResult {
+  ast: Send {
+    recv: Int {
+      value: '2',
+      operator_l: null,
+      expression_l: Range { begin_pos: 0, end_pos: 1 }
+    },
+    method_name: '+',
+    args: [
+      Int {
+        value: '3',
+        operator_l: null,
+        expression_l: Range { begin_pos: 4, end_pos: 5 }
+      }
+    ],
+    dot_l: null,
+    selector_l: Range { begin_pos: 2, end_pos: 3 },
+    begin_l: null,
+    end_l: null,
+    operator_l: null,
+    expression_l: Range { begin_pos: 0, end_pos: 5 }
+  },
+  tokens: [
+    Token {
+      name: 'tINTEGER',
+      value: '2',
+      loc: Loc { begin: 0, end: 1 }
+    },
+    Token { name: 'tPLUS', value: '+', loc: Loc { begin: 2, end: 3 } },
+    Token {
+      name: 'tINTEGER',
+      value: '3',
+      loc: Loc { begin: 4, end: 5 }
+    },
+    Token { name: 'EOF', value: '', loc: Loc { begin: 5, end: 5 } }
+  ],
+  diagnostics: [],
+  comments: [],
+  magic_comments: [],
+  input: '2 + 3'
+}
+```
+
+## API
+
+tldr; all classes mirror Rust implementation.
+
+TypeScript definition:
+
+```ts
+interface Loc { begin: number, end: number }
+interface Range { begin_pos: number, end_pos: number }
+
+interface Token {
+    name: string,
+    value: string,
+    loc: Loc
+}
+
+interface Args {
+    // mirrors https://docs.rs/lib-ruby-parser/0.7.0/lib_ruby_parser/nodes/struct.Args.html
+    args: Array<Node>,
+    expression_l: Range,
+    begin_l: Range | null,
+    end_l: Range | null
+}
+
+interface Class {
+    // mirrors https://docs.rs/lib-ruby-parser/0.7.0/lib_ruby_parser/nodes/struct.Class.html
+    name: Node,
+    superclass: Node | null,
+    body: Node | null,
+    keyword_l: Range,
+    operator_l: Range | null,
+    end_l: Range,
+    expression_l: Range
+}
+
+// other ~100 nodes
+
+type Node = Args | Class | ... /* other nodes */;
+
+function parse(code: String): ParserResult
+```