Add rootUrl to links.

doc/src/about/non-design.md

@@ -1 +1,33 @@
-# What Rhai Doesn't Do
+What Rhai Doesn't Do
+====================
+
+{{#include ../links.md}}
+
+Rhai's purpose is to provide a dynamic layer over Rust code, in the same spirit of _zero cost abstractions_.
+It doesn't attempt to be a new language. For example:
+
+* No classes.  Well, Rust doesn't either. On the other hand...
+
+* No traits...  so it is also not Rust. Do your Rusty stuff in Rust.
+
+* No structures/records - define your types in Rust instead; Rhai can seamlessly work with _any Rust type_.
+  There is, however, a built-in [object map] type which is adequate for most uses.
+
+* No first-class functions - Code your functions in Rust instead, and register them with Rhai.
+
+* No garbage collection - this should be expected, so...
+
+* No closures - do your closure magic in Rust instead; [turn a Rhai scripted function into a Rust closure]({{rootUrl}}/engine/call-fn.md).
+
+* No byte-codes/JIT - Rhai has an AST-walking interpreter which will not win any speed races. The purpose of Rhai is not
+  to be extremely _fast_, but to make it as easy as possible to integrate with native Rust programs.
+
+Due to this intended usage, Rhai deliberately keeps the language simple and small by omitting advanced language features
+such as classes, inheritance, first-class functions, closures, concurrency, byte-codes, JIT etc.
+
+Avoid the temptation to write full-fledge program logic entirely in Rhai - that use case is best fulfilled by
+more complete languages such as JS or Lua.
+
+Therefore, in actual practice, it is usually best to expose a Rust API into Rhai for scripts to call.
+All your core functionalities should be in Rust.
+This is similar to some dynamic languages where most of the core functionalities reside in a C/C++ standard library.