Add 'tips for map makers' manual page

[joskuijpers]

Do:

• Use different trees
• Use random rotation of trees
• Use trees and bushes from Goldcrest or Sosnovka for the texture replacement to work seamlessly. If not add season specific textures for other trees and bushes
• Paint as many roads as possible to allow them to be ploughable (both to make fields, and for snow)
• Make some foliage season specific (i.e. foliage that normally grows in spring, summer and autumn, but not in winter)
• Adhere to Giants conventions
  • Adjust / add onto existing specializations, instead of writing your own

Don't:

• Make your own objects when you can use Giants conventions (bales, wrapped state, etc)

• Try to avoid overwriting a whole (vanilla) function, and attempt to append and prepend whenever possible

• If you overwrite a vanilla function, use the superFunc call.

• If you can't (like in our startMotor/stopMotor), make sure it works with all existing big mods: test it.