udate api doc for resolving auto inertia

Signed-off-by: Ian Chen <[email protected]>

include/sdf/Link.hh

@@ -351,9 +351,12 @@ namespace sdf
                                    const std::string &_resolveTo = "") const;
 
     /// \brief Calculate & set inertial values(mass, mass matrix
-    /// & inertial pose) for the link. Inertial values can be provided
-    /// by the user through the SDF or can be calculated automatically
-    /// by setting the auto attribute to true.
+    /// & inertial pose) for the link. This function will calculate
+    /// the inertial values if the auto attribute is set to true.
+    /// If mass is not provided by the user, the inertial values will be
+    /// determined based on either link density or collision density if
+    /// explicitly set. Otherwise, if mass is specified, the inertia matrix
+    /// will be scaled to match the desired mass.
     /// \param[out] _errors A vector of Errors object. Each object
     /// would contain an error code and an error message.
     /// \param[in] _config Custom parser configuration