Make even clearer that pkg-config has to first work before anything else will.

doc/chapters/basic-examples.texi

@@ -38,6 +38,10 @@ LDFLAGS         +=      $$(pkg-config --libs starpu-1.0)
 @end example
 @end cartouche
 
+Make sure that @code{pkg-config --libs starpu-1.0} actually produces some output
+before going further: @code{PKG_CONFIG_PATH} has to point to the place where
+@code{starpu-1.0.pc} was installed during @code{make install}.
+
 Also pass the @code{--static} option if the application is to be linked statically.
 
 @node Hello World
@@ -55,8 +59,8 @@ Extensions}) or directly use the StarPU's API.
 @node Hello World using the C Extension
 @subsection Hello World using the C Extension
 
-Writing a task is both simpler and less error-prone when using the C
-extensions implemented by StarPU's GCC plug-in (@pxref{C Extensions}).
+GCC from version 4.5 permit to use the StarPU GCC plug-in (@pxref{C
+Extensions}). This makes writing a task both simpler and less error-prone.
 In a nutshell, all it takes is to declare a task, declare and define its
 implementations (for CPU, OpenCL, and/or CUDA), and invoke the task like
 a regular C function.  The example below defines @code{my_task}, which