Better commenting throughout

internal/projectile/projectile.go

@@ -7,6 +7,8 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/vector"
 )
 
+// Projectile configuration
+
 type ProjectileConfig struct {
 	Speed  float64
 	Radius float64
@@ -58,6 +60,8 @@ func (p *Projectile) Draw(screen *ebiten.Image) {
 	)
 }
 
+// Projectile manager
+
 type Manager struct {
 	Projectiles []*Projectile
 }