revise usage of key_nosignedzero in chap_misc

latex/NEMO/subfiles/chap_misc.tex

@@ -266,7 +266,8 @@ so we overwrite the intrinsinc function with our own function simply performing
 \verb?   IF( B >= 0.e0 ) THEN   ;   SIGN(A,B) = ABS(A)  ?    \\
 \verb?   ELSE                   ;   SIGN(A,B) =-ABS(A)     ?  \\
 \verb?   ENDIF    ? \\
-This feature can be found in \mdl{lib\_fortran} module and is effective when \key{nosignedzero} is defined.
+This feature can be found in \mdl{lib\_fortran} module and it is effective when the macro \key{nosignedzero} 
+is defined within the cpp file of the configuration.
 We use a CPP key as the overwritting of a intrinsic function can present performance issues with
 some computers/compilers.