doc: add missing documentation

doc/chapters/configuration.texi

@@ -279,6 +279,11 @@ MKL website} provides a script to determine the linking flags.
 Disable the build of examples.
 @end defvr
 
+@defvr {Configure option} --enable-memory-status
+Enable the display of memory status at the end of the execution
+(@pxref{Memory feedback}).
+@end defvr
+
 @node Execution configuration through environment variables
 @section Execution configuration through environment variables
 
@@ -536,3 +541,8 @@ as it emulates devices that have a limited amount of memory.
 When set to 1, this variable indicates that StarPU should automatically
 generate a Paje trace when starpu_shutdown is called.
 @end defvr
+
+@defvr {Environment variable} STARPU_MEMORY_STATUS
+Enable the display of memory status at the end of the execution
+(@pxref{Memory feedback}).
+@end defvr