documentation for level builders: docs index, step-by-step guide, file format reference (wad, geometry, objects, textures, audio, testlevel chapters, engine limits), strat vm and script language with the arena as worked example, tools overview, developer notes; readme rewritten as project front page with screenshots; review notes moved to notes/dev

notes/editor-tools-environment.md

@@ -5,7 +5,7 @@ Code: `src/main/java/com/eliasmueller/llamamod/editor/tools/environment/`, tests
 `src/test/.../editor/tools/environment/` (`EnvironmentToolsTest` needs `-Dllamamod.cd`; `EnvTour`
 = scripted screenshots, `EnvScenarios` = the in-game test projects).
 
-![zones](img/editor/env_zones.jpg)
+![zones](img/editor/env_zone.jpg)
 
 ## What the user gets