Update documentation for body system code (#2556)

Content.Shared/GameObjects/Components/Body/Part/Property/ExtensionComponent.cs

@@ -3,13 +3,16 @@ using Robust.Shared.Serialization;
 
 namespace Content.Shared.GameObjects.Components.Body.Part.Property
 {
+    /// <summary>
+    ///     Defines the length of a <see cref="IBodyPart"/>.
+    /// </summary>
     [RegisterComponent]
     public class ExtensionComponent : BodyPartPropertyComponent
     {
         public override string Name => "Extension";
 
         /// <summary>
-        ///     Current distance (in tiles).
+        ///     Current distance in tiles.
         /// </summary>
         public float Distance { get; set; }