Category option for signature (#343)

* category option for signature

* category option for signature

* column description for $scope

crates/nu-command/src/conversions/into/binary.rs

@@ -2,7 +2,7 @@ use nu_engine::CallExt;
 use nu_protocol::{
     ast::{Call, CellPath},
     engine::{Command, EngineState, Stack},
-    Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Value,
+    Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Value,
 };
 
 #[derive(Clone)]
@@ -14,11 +14,13 @@ impl Command for SubCommand {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("into binary").rest(
-            "rest",
-            SyntaxShape::CellPath,
-            "column paths to convert to binary (for table input)",
-        )
+        Signature::build("into binary")
+            .rest(
+                "rest",
+                SyntaxShape::CellPath,
+                "column paths to convert to binary (for table input)",
+            )
+            .category(Category::Conversions)
     }
 
     fn usage(&self) -> &str {