Translations:Add FEM Equation Tutorial/9/en

Next, the command/equation has to be added to the module. Just copy an existing command and adjust the icon, menu text and tool-tip in __init__(self). Don't forget to register the command at the bottom of the module file by using the addCommand(...) method. Please see the discussion in the forum at https://forum.freecadweb.org/viewtopic.php?f=18&t=46693&start=10#p402004 if icons are involved.