doc: Update description of APP and TEST scopes

Co-authored-by: Laurence Kedward <[email protected]>

Author: everythingfunctional

fpm/src/fpm_targets.f90

@@ -329,8 +329,8 @@ end subroutine add_dependency
 !>
 !> - Executable sources (`FPM_SCOPE_APP`,`FPM_SCOPE_TEST`) may use
 !>   library modules (including dependencies) as well as any modules
-!>   corresponding to source files __in the same directory__ as the
-!>   executable source.
+!>   corresponding to source files in the same directory or a 
+!>   subdirectory of the executable source file.
 !>
 !> @warning If a module used by a source file cannot be resolved to
 !> a source file in the package of the correct scope, then a __fatal error__