update config

Author: m1dnight

README.md

@@ -3,9 +3,67 @@
 EnvConfig is a library that makes it easier to write `runtime.exs` files that take in parameters
 from the environment.
 
-The idea is that EnvConfig allows you to define which environment variables an application needs,
+The idea is that `EnvConfig` allows you to define which environment variables an application needs,
 what their type is expected to be, and whether they are optional for the application to start.
 
+The api ensures that the values are read from the environment and are cast into their proper Elixir types.
+
+**Before**
+```elixir
+import Config
+
+if config_env() == :prod do
+  secret_key_base =
+    System.get_env("SECRET_KEY_BASE") ||
+      raise """
+      environment variable SECRET_KEY_BASE is missing.
+      You can generate one by calling: mix phx.gen.secret
+      """
+
+  if System.get_env("PHX_SERVER") do
+    config :my_app, MyAppWeb.Endpoint, server: true
+  end
+end
+```
+
+**After**
+
+```elixir
+import Config
+require EnvConfig.Macros
+import EnvConfig.Macros
+
+if config_env() == :prod do
+  secret_key_base = required("SECRET_KEY_BASE", :string, min_length: 64)
+
+  phx_server = optional("PHX_SERVER", :boolean, false)
+  config :my_app, MyAppWeb.Endpoint, server: phx_server
+end
+```
+
+If the environment variable is not defined, you will see the same error.
+
+```text
+** (RuntimeError) Environment variable SECRET_KEY_BASE is not set
+    /Users/christophe/Documents/Code/loomy/data-api/config/runtime.exs:5: (file)
+    (stdlib 6.2) erl_eval.erl:919: :erl_eval.do_apply/7
+    (stdlib 6.2) erl_eval.erl:663: :erl_eval.expr/6
+    (stdlib 6.2) erl_eval.erl:271: :erl_eval.exprs/6
+    (elixir 1.18.1) lib/code.ex:572: Code.validated_eval_string/3
+```
+
+Or, when the type or constraints are not met, an error explaining whats wrong.
+
+```text
+** (RuntimeError) Environment variable SECRET_KEY_BASE does not meet constraints. string is shorter than 64 characters
+    /Users/christophe/Documents/Code/loomy/data-api/config/runtime.exs:5: (file)
+    (stdlib 6.2) erl_eval.erl:919: :erl_eval.do_apply/7
+    (stdlib 6.2) erl_eval.erl:663: :erl_eval.expr/6
+    (stdlib 6.2) erl_eval.erl:271: :erl_eval.exprs/6
+    (elixir 1.18.1) lib/code.ex:572: Code.validated_eval_string/3
+```
+
+
 ## Installation
 
 The package can be installed
@@ -21,15 +79,16 @@ end
 
 ## Types
 
-  - `:boolean`
-  - `:integer`
-    - Constraints
-      - `{:min, integer}`: minimal required value
-      - `{:max, integer}`: maximal required value
-  - `:string`
-    - Constraints
-      - `{:allow_empty?, boolean}`: allow the (trimmed) string to be empty
-      - `{:min_length, integer}`: minimal length of the string
-      - `{:max_length, integer}`: maximum length of the string
-
-## Example
+EnvConfig supports basic types out of the box, and lists of these types.
+
+| Type                | Values                                                                       | Elixir Type  |
+|---------------------|------------------------------------------------------------------------------|--------------|
+| `:boolean`          | `true`, `TRUE`, `1`, `false`, `FALSE`, `0`                                   | `boolean()`  |
+| `:string`           | any value                                                                    | `String.t()` |
+| `:atom`             | any value                                                                    | `atom()`     |
+| `charlist`          | any value                                                                    | `charlist()` |
+| `integer`           | any integral value that's parsable as an integer using `&Integer.parse/1`    | `integer()`  |
+| `:float`            | any value that's parsable as a float using `&Float.parse/1`                  | `float()`    |
+| `{:list, type}`     | a comma-separated list of values for any given type in the above table.      | `[type]`     |
+| `{:enum, [binary]}` | any value that is a member of the values given in the list of the enum type. | `String.t()` |
+|---------------------|------------------------------------------------------------------------------|--------------|