Step 1

1)  Open weapons.qc
2)  find W_FireLightning
3)  Replace the Entire Funstion with this new function below

void() W_FireLightning =
{
	local	entity thunderbolt; // create thunderbolt entity

    if (self.ammo_cells < 1) // if u have more than 1 cell, this is the best weapon
	{
		self.weapon = W_BestWeapon ();
		W_SetCurrentAmmo ();
			return;
	}
	self.currentammo = self.ammo_cells = self.ammo_cells - 1; // ammo it uses
	self.punchangle_x = -2; // kickback angle
	thunderbolt = spawn (); // spawning it
	thunderbolt.owner = self; // self (you) is owner of thunderbolt
	thunderbolt.movetype = MOVETYPE_FLYMISSILE; // flies straight on
	thunderbolt.solid = SOLID_BBOX; // its solid
	thunderbolt.classname = "thunderbolt"; // name it thunderbolt
	makevectors (self.v_angle); // i dont know
	thunderbolt.velocity = aim(self, 1000); // dont know this either
	thunderbolt.velocity = thunderbolt.velocity * 1000; //speed of 1000
	thunderbolt.angles = vectoangles(thunderbolt.velocity); // dont know
	thunderbolt.touch = LightningHit; // calls LightningHit when touched
	thunderbolt.nextthink = time + 5; // disappears after flying for 5 seconds
	thunderbolt.think = SUB_Remove; // does nothing after 5 seconds
	setmodel (thunderbolt, "progs/bolt.mdl"); // sets the thunderbolt model
	setsize (thunderbolt, '0 0 0', '0 0 0'); // thunderbolt model size
	setorigin (thunderbolt, self.origin + v_forward*8 + '0 0 16'); // thunderbolt spawn origin
};

void() LightningHit =
{        
	local	vector org; // creates org vector
	local	float damage=0; // floats damage starting at 0
	local	entity head; //creates head entity

	org = self.origin + '0 0 16'; // vector org origin
	head = findradius(self.origin, 250); //send lightning line to anything in 250 radius
	while (head) // while looking for head
	{
		if (head.takedamage)  // if head has health, attack it
		{
			if(head != self.owner) // don't attack thunderbolt owner!!
            {
				WriteByte (MSG_BROADCAST, SVC_TEMPENTITY); // temp entity
				WriteByte (MSG_BROADCAST, TE_LIGHTNING2); // makes lightning line i think
				WriteEntity (MSG_BROADCAST, head); // write head entity
				WriteCoord (MSG_BROADCAST, org_x); // write orgs x coord
				WriteCoord (MSG_BROADCAST, org_y); // write orgs y coord
				WriteCoord (MSG_BROADCAST, org_z); // write orgs z coord
				WriteCoord (MSG_BROADCAST, head.origin_x); // write heads x coord
				WriteCoord (MSG_BROADCAST, head.origin_y); // write heads y coord
				WriteCoord (MSG_BROADCAST, head.origin_z); // write heads z coord
				sound (head, CHAN_WEAPON, "weapons/lhit.wav", 1, ATTN_NORM); // its sound
				damage = 40 + random()*20; // 40 plus some random damage
				T_Damage (head, self, self.owner, damage); // its damage
			}
		}
        head = head.chain; // go to next enemy
	}
        remove(self);
};