Fix confusion in Translation Units doc (#4245)

I think the sentence was saying the opposite of what it meant!

Co-authored-by: Yong He <[email protected]>

docs/user-guide/08-compiling.md

@@ -31,7 +31,7 @@ Note that the `#include`d files do not become additional source units; they are
 Source units (such as files) are grouped into _translation units_, and each translation unit will produce a single _module_ when compiled.
 
 While the source units are all preprocessed and parsed independently, semantic checking is applied to a translation unit as a whole.
-One source file in a translation unit may freely refer to declarations in another translation unit without any need for forward declarations. For example:
+One source file in a translation unit may freely refer to declarations in another source file from the same translation unit without any need for forward declarations. For example:
 
 ```hlsl
 // A.slang