Docs: Add missing directories in readme.md (#11006)

Add missing directories in the source directory structure readme, with a short description to each. Additionally, change the order of 'management' and 'order' such that they are now in alphabetical order.

src/openrct2/readme.md

@@ -1,9 +1,25 @@
 # Source directory structure
 
+- **actions**
+
+  Handles player actions and queues pending actions.
+
 - **audio**
 
   Contains files for mixing and playing music and sound.
 
+- **cmdline**
+
+  Code specific to command line (arguments).
+
+- **config**
+
+  Code concerning game configuration.
+
+- **core**
+
+  Provides core functionality such as string operations, encryption, and compression.
+
 - **drawing**
 
   Low level drawing logic and palette tables.
@@ -16,13 +32,21 @@
 
   String IDs, currency and date logic.
 
+- **management**
+
+  Park management logic such as finance, marketing and research.
+
 - **network**
 
   Network and multiplayer logic, includes management of network games and downloading / uploading of content.
 
-- **management**
+- **object**
 
-  Park management logic such as finance, marketing and research.
+  Code relating to objects (rides, shops, scenery, etc).
+
+- **paint**
+
+  Prepares objects' sprites to be drawn.
 
 - **peep**
 
@@ -32,10 +56,30 @@
 
   Compiler and operating system specific code such as type definitions, message handling and file input / output.
 
+- **rct1**
+
+  Code specific only to RCT1 (vanilla).
+
+- **rct2**
+
+  Code specific only to RCT2 (vanilla).
+
+- **rct12**
+
+  Code specific to vanilla RCT, either RCT 1 or RCT 2.
+
 - **ride**
 
   Data and logic for rides, vehicles and track.
 
+- **scenario**
+
+  Code relating to game scenarios.
+
+- **title**
+
+  Code for loading and updating title screen sequence.
+
 - **util**
 
   Utility and helper functions.
@@ -47,3 +91,4 @@
 - **world**
 
   World objects and mechanics such as the climate, landscape, sprites and park.
+