add README.md

Author: andrei.lepeshkin

README.md

@@ -0,0 +1,20 @@
+# JSONRPC2Plug
+
+JSONRPC 2 plug
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `jsonrpc2_plug` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:jsonrpc2_plug, "~> 0.1.0"}
+  ]
+end
+```
+
+Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
+and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
+be found at [https://hexdocs.pm/jsonrpc2_plug](https://hexdocs.pm/jsonrpc2_plug).