Add positive shift example

Author: Rupt

README.md

@@ -25,6 +25,7 @@ Standard integer types are supported for pedantic C99.
 sari(-63, 3); /* -8 */
 sarl(-0x200000000l, 1); /* -0x100000000l */
 sarfast32(-0xDECAF, 8); /* -0xDED */
+sar8(15, 2); /* 3 */
 ```
 
 <details>

test.c

@@ -112,10 +112,12 @@ main()
  assert(sari(-63, 3) == -8);
  assert(sarl(-0x200000000l, 1) == -0x100000000l);
  assert(sarfast32(-0xDECAF, 8) == -0xDED);
+ assert(sar8(15, 2) == 3);
 
  assert(sarui(-63, 3) == -8);
  assert(sarul(-0x200000000l, 1) == -0x100000000l);
  assert(sarufast32(-0xDECAF, 8) == -0xDED);
+ assert(saru8(15, 2) == 3);
 
  return 0;
 }