Fix rst readme

Author: sergey-dryabzhinsky

README.rst

@@ -516,7 +516,7 @@ ZSTD_version_number (): int
 
 ZSTD_threads_count (): int
   Returns ZSTD determined CPU cores count.
- Better to get this nuber as early as possible befor compression starts.
+  Better to get this nuber as early as possible befor compression starts.
 
   Since: 1.5.4.1