Additional loading screen tips

[elexis]

There are some game features that even experienced players don't know about. We should add loading screen tips explaining those. These consist of a text file in gui/text/tips and an image file with the same base name in art/textures/ui/loading/tips/.

Below is a list of topics needing some explanation and some relevant information. Note that certain topics might need multiple tips. Note that the categories need not be this way so if you have another way of arranging them (eg something about dropsites) go for it.

• Barter
  • Rates are global, so a player watching them can turn a profit by exchanging resources.
  • Exchanges one resource for another at the rate listed there.
  • Requires a market (or is done at one)
• Loot
  • Killing units gives some resources
  • Killing trade carts loots the resources they carry.
• Mauryan Worker Elephant
  • Resource dropsite (can be used to gather outside of your territory)
  • Can help construct buildings
• Dock
  • Dropsite for all resources (also for land units)
  • Build ships
  • Can be built outside of own territory
• Nomad Mode
  • Start without a CC
  • Can build that where you want
  • Use a dock to gather resources early without placing the CC (if not enough resources)
• Trade
  • Trade routes between two markets (or one market and a dock, or two docks)
  • Merchant Ships and Traders can open trade routes
  • You can trade with yourself, but trading with an ally or a neutral player is better. The other player will get a share of the traded resources, but there is a gain bonus too.
  • Trade routes are set by selecting a trader and the right-clicking on two markets.
  • The ratio of traded resources can be set in the trading dialog at the top left.
  • The profit increases with the distance, thus markets should be built as far apart as possible.
  • At some distance trade carts generate income faster than the same amount of men gathering resources. So this is a good way to get resources in late-game.
  • Trading with carts from a market to a dock helps with increasing the distance.
  • Enemy trade routes are a valuable target since they should be quite long and hard to defend, and you both get some loot, and deal their economy a blow.

[leper]

The looting related parts could be one tip, that also explains #2732.

[elexis]

• 'Barter efficiency also needs a tooltip!:
• Market profits can be optimized by setting the currently most requested resource as trading good and then selling this for the resources you actually need.

This way you can often have a barter efficiency > 100%, i.e. getting profit.

Notice if all players do that, then you won't be able to barter any resource with profit.