Small cleanups (2)

- fix a small compile error under MSVC
- improve sigmoid comment and assert
- fix formatting in README.md

closes https://github.com/official-stockfish/Stockfish/pull/3960

No functional change

src/misc.h

@@ -152,7 +152,7 @@ private:
 ///  -  the slope can be adjusted using C > 0, smaller C giving a steeper sigmoid
 ///  -  the slope of the sigmoid when t = x0 is P/(Q*C)
 ///  -  sigmoid is increasing with t when P > 0 and Q > 0
-///  -  to get a decreasing sigmoid, call with -t, or change sign of P
+///  -  to get a decreasing sigmoid, change sign of P
 ///  -  mean value of the sigmoid is y0
 ///
 /// Use <https://www.desmos.com/calculator/jhh83sqq92> to draw the sigmoid
@@ -163,7 +163,8 @@ inline int64_t sigmoid(int64_t t, int64_t x0,
                                   int64_t  P,
                                   int64_t  Q)
 {
-   assert(C > 0 && Q != 0);
+   assert(C > 0);
+   assert(Q != 0);
    return y0 + P * (t-x0) / (Q * (std::abs(t-x0) + C)) ;
 }