problem on adding hand v1_2_research on an existing urdf

adding the hand to an existing urdf it gives me the error: "unknown macro name: xacro:softhand_mimic_plugin".
To solve I added ```<xacro:include filename="$(find softhands_description)/urdf/xacro/include/macro/plugin.xacro"/>``` after line 40 of file `src/SoftHand-Plugin/softhands_description/urdf/xacro/v1_2_research.xacro`.
I do not know if this is the right way but the hand is now spawned.

