add sleepingmask to how to survive

docs/how-to-survive.md

@@ -7,6 +7,7 @@
 * stable tent pegs (best use v-profile ones)
 * a sleeping bag
 * a mattress and a sleeping pad. Maybe a cushion.
+* a sleeping mask if you are sensitive to light.
 * a drinking bottle. Drink more water - drinking not enough (water! not mate, not beer!) is the most common DoS-Attack at camps.
 * a rescue blanket: One of those silvery blankets you find in first aid kits. They are very good at reflecting sunlight away from your computer monitor, so you'll be able to hack during the day. Most tents let in a *lot* of light and rescue blankets are one of the cheaper ways to fix that.
 * blanket to sit on and place your laptop on. You might not want to sit on a dew covered ground in the morning