[numerics.general] Add library summary entry

Author: tkoeppe

source/numerics.tex

@@ -25,7 +25,8 @@
 \ref{c.math}  & Mathematical functions for floating-point types &
   \tcode{<cmath>}, \tcode{<cstdlib>} \\ \rowsep
 \ref{numbers}  & Numbers & \tcode{<numbers>} \\ \rowsep
-\ref{linalg}   & Linear algebra & \tcode{<linalg>} \\
+\ref{linalg}   & Linear algebra & \tcode{<linalg>} \\ \rowsep
+\ref{simd}     & Data-parallel types & \tcode{<simd>} \\
 \end{libsumtab}
 
 \rSec1[numeric.requirements]{Numeric type requirements}