add readme

README.md

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+# kojima
+a small functional/monad library
+
+# Usage
+## Example
+```js
+import { Identity, Some, None, Left, Right, Ok, Err } from 'kojima'
+
+const i = Identity(1)
+const thou = Identity(1)
+i.bind(x => thou.map(y => x + y)) // Identity(2)
+
+const maybe = Some('thing')
+maybe.isSome() // true
+const isnt = maybe.bind(() => None).map(_x => 'other') // None
+isnt.isSome() // false
+
+const either = Right('neutron')
+
+const value = either.match({
+    Right(value) {
+        return value
+    },
+    Left(value) {
+        console.error('oh no')
+    }
+}) // 'neutron'
+
+const result = Ok('3:41am')
+result.isOk() // true
+
+result.bind(() => new Error(-Infinity))
+    .map(_x => '4:10am')
+
+result.isErr() // true
+```
+