docs: Preliminary changelog for v3.0.0

Author: Clashsoft

docs/Changelog.md

@@ -137,3 +137,25 @@
 ## Documentation
 
 * Improved the `403 Forbidden` error documentation for updating a running game.
+
+# v3.0.0 (2024-06-XX)
+
+## BREAKING CHANGES
+* Game ticks are no longer scheduled and must be trigger via `PATCH /games/:game?tick=true`.
+* Changed the `empire.pop.credits.unemployed` variable to `empire.pop.unemployed_upkeep.credits`.
+
+## New Features
+* Custom effects with `base` values can now create new variables, in the following contexts:
+  * Building and district cost, upkeep and production.
+  * System upgrade upkeep.
+  * System type district chances.
+  * Pop consumption.
+  * Unemployed pop costs.
+
+## Improvements
+* Game speed can be any positive number number.
+  It must be interpreted by the client to trigger manual ticks.
+* The `PATCH /games/:game` request that starts a game now waits until the game is properly initialized before responding.
+
+## Bugfixes
+* Fixed some situations where systems may not be connected to the rest of the map.