Update README.md

Author: arithy

README.md

@@ -45,6 +45,7 @@ You can install the development version by the following commands.
 ```sh
 $ cd softfloatpy  # the repository root directory
 $ make req
+$ make clean
 $ make dist
 $ python -m pip install --no-index --find-links=./dist softfloatpy
 ```