update documentation and error message

Author: bdebinska

README.md

@@ -1,21 +1,16 @@
 # ValueFormatters
 
-**TODO: Add description**
+## Usage
 
-## Installation
+To use value formatters, the host application needs to set up its own Cldr backend, including the following libraries:
 
-If [available in Hex](https://hex.pm/docs/publish), the package can be installed
-by adding `value_formatters` to your list of dependencies in `mix.exs`:
+* Cldr.Number,
+* Cldr.Calendar,
+* Cldr.DateTime,
+* Cldr.Time,
+* Cldr.Date
+
+Cldr needs to be passed as an option to the `to_string/3` method under `cldr` key.
 
-```elixir
-def deps do
-  [
-    {:value_formatters, "~> 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/value_formatters>.
 

lib/value_formatters.ex

@@ -118,7 +118,8 @@ defmodule ValueFormatters do
     else
       :error ->
         raise ArgumentError,
-          message: "The :cldr option is required."
+          message:
+            "Attempted to access a Cldr module, but non was specified. Pass the :cldr option to to_string/3 or when instantiating the module."
     end
   end
 

test/cldr.ex

@@ -10,7 +10,6 @@ defmodule ValueFormatters.Cldr do
       Cldr.Calendar,
       Cldr.DateTime,
       Cldr.Time,
-      Cldr.Date,
-      Cldr.List
+      Cldr.Date
     ]
 end

test/value_formatters_test.exs

@@ -624,9 +624,11 @@ defmodule ValueFormattersTest do
 
   describe "missing cldr" do
     test "returns error when cldr is not available" do
-      assert_raise ArgumentError, "The :cldr option is required.", fn ->
-        ValueFormatters.to_string(1.234, %{"format" => "number"}, [])
-      end
+      assert_raise ArgumentError,
+                   "Attempted to access a Cldr module, but non was specified. Pass the :cldr option to to_string/3 or when instantiating the module.",
+                   fn ->
+                     ValueFormatters.to_string(1.234, %{"format" => "number"}, [])
+                   end
     end
   end
 end