docs(args): Clarify what args are esclusive

src/args.rs

@@ -41,6 +41,7 @@ impl Default for Format {
         setting = structopt::clap::AppSettings::DeriveDisplayOrder,
         setting = structopt::clap::AppSettings::DontCollapseArgsInUsage
     )]
+#[structopt(group = structopt::clap::ArgGroup::with_name("mode").multiple(false))]
 pub(crate) struct Args {
     #[structopt(parse(from_os_str), default_value = ".")]
     /// Paths to check with `-` for stdin
@@ -54,23 +55,23 @@ pub(crate) struct Args {
     /// Ignore implicit configuration files.
     pub(crate) isolated: bool,
 
-    #[structopt(long)]
+    #[structopt(long, group = "mode")]
     /// Print a diff of what would change
     pub(crate) diff: bool,
 
-    #[structopt(long, short = "w")]
+    #[structopt(long, short = "w", group = "mode")]
     /// Write fixes out
     pub(crate) write_changes: bool,
 
-    #[structopt(long)]
+    #[structopt(long, group = "mode")]
     /// Debug: Print each file that would be spellchecked.
     pub(crate) files: bool,
 
-    #[structopt(long)]
+    #[structopt(long, group = "mode")]
     /// Debug: Print each identifier that would be spellchecked.
     pub(crate) identifiers: bool,
 
-    #[structopt(long)]
+    #[structopt(long, group = "mode")]
     /// Debug: Print each word that would be spellchecked.
     pub(crate) words: bool,