[Backport] Fix setting environment vars in readme (#63)

* Remove spaces from environment variable setting because it only works without spaces

(cherry picked from commit MeVisLab/pythonqt@aa132d2)

Author: githubuser0xFFFF

README.md

@@ -43,7 +43,7 @@ the directory where the python lib file is located. Then you should set the
 When using the prebuild Python installer, this will be:
 
 ```cmd
-set PYTHON_PATH = c:\Python38
-set PYTHON_LIB  = c:\Python38\libs
-set PYTHON_VERSION = 38
-```
+set PYTHON_PATH=c:\Python38
+set PYTHON_LIB=c:\Python38\libs
+set PYTHON_VERSION=38
+```