Add environment fallback for config path

+ FORMATY_CONFIG is the fallback for the optional config path
+ If -c is not provided, we go to the system config

README.md

@@ -64,20 +64,20 @@ Formaty 0.1.0
 Arbitrary Binary Data Formatting
 
 USAGE:
-formaty [OPTIONS] <format> [data]...
+    formaty [OPTIONS] <format> [data]...
 
 FLAGS:
--h, --help       Prints help information
--V, --version    Prints version information
+    -h, --help       Prints help information
+    -V, --version    Prints version information
 
 OPTIONS:
--b, --base <base>                Base of the input values
--c, --config <config>            Path to the format config
--i, --input_type <input-type>    Input data type [default: array]
+    -b, --base <base>                Base of the input values
+    -c, --config <config>            Path to the format config [env: FORMATY_CONFIG=]
+    -i, --input_type <input-type>    Input data type [default: array]
 
 ARGS:
-<format>     Format to parse data as
-<data>...    Raw data
+    <format>     Format to parse data as
+    <data>...    Raw data
 ```
 
 ## License

src/main.rs

@@ -16,6 +16,7 @@ pub struct Args {
     #[structopt(
         short = "c",
         long = "config",
+        env = "FORMATY_CONFIG",
         parse(from_os_str),
         help = "Path to the format config"
     )]