I think you can only embed the table not the whole spreadsheet
Click the Advanced reply option, copy and paste the table

Map # Level Reqd Map Target Energy Hits Total Energy xp per hit Total xp Event
1 1 Insurgent Camp Grunt Deadly Soldier 5 5 25 1 5 Deadly Race LTQ
1 1 Insurgent Camp Grunt Deadly Warrior 5 22 110 3 15 Deadly Race LTQ
1 1 Insurgent Camp Grunt Deadly Agent 5 60 300 6 30 Deadly Race LTQ