docs: add example instances and changelog

examples/sat.cnf

@@ -0,0 +1,7 @@
+c sample satisfiable formula
+c (x1 or x2 or -x3) and (-x1 or x3) and (-x2 or x3) and (x1 or x2)
+p cnf 3 4
+1 2 -3 0
+-1 3 0
+-2 3 0
+1 2 0