docs: add comment on different tolerance

Author: gunjjoshi

lib/node_modules/@stdlib/math/base/special/riemann-zeta/test/test.js

@@ -163,7 +163,7 @@ tape( 'the function handles negative integer values which are larger in magnitud
 	s = -259;
 	v = zeta( s );
 	delta = abs( v - expected );
-	tol = 656.0 * EPS * abs( expected );
+	tol = 352.0 * EPS * abs( expected );
 
 	t.ok( delta <= tol, 'within tolerance. s: '+s+'. v: '+v+'. E: '+expected+' Δ: '+delta+'. tol: '+tol );
 

lib/node_modules/@stdlib/math/base/special/riemann-zeta/test/test.native.js

@@ -172,6 +172,8 @@ tape( 'the function handles negative integer values which are larger in magnitud
 	s = -259;
 	v = zeta( s );
 	delta = abs( v - expected );
+
+	// NOTE: the tolerance here is larger than for the JavaScript implementation due to compiler optimizations which may be performed resulting in result divergence. For discussion, see https://github.com/stdlib-js/stdlib/pull/2298#discussion_r1624765205
 	tol = 656.0 * EPS * abs( expected );
 
 	t.ok( delta <= tol, 'within tolerance. s: '+s+'. v: '+v+'. E: '+expected+' Δ: '+delta+'. tol: '+tol );