Properly link flecs library

engine/libs/flecs/examples/plecs/docs.flecs

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+// To see what the result of parsing this file looks like, copy the code and
+// paste it into the editor at https://flecs.dev/explorer
+//
+// To load this file yourself, call ecs_plecs_from_file("docs.flecs");
+
+// Plecs files can be used to annotate entities and components with 
+// documentation. These annotations use the flecs.doc addon.
+
+@brief A brief description of planet Earth
+@name The Earth
+Earth {
+  - Planet
+}
+
+// Annotations can be created for entities definfed elsewhere. This makes it
+// possible to have a file separate from source code where you annotate your
+// prefabs, components and entities with documentation
+
+@brief The Position component
+Position