Installation error (permissions): suggestion for readme/instructions

[tomakkermans]

During installation, i got an error concerning access permissions (see below).
It would be good to at least warn users for this, or provide the alternative code including the -H flag.
Best regards, thanks, and keep up the good work!

tom@tom-linux:~$ sudo pip3 install git+https://github.com/serialoverflow/blockify
[sudo] password for tom:
The directory '/home/tom/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/home/tom/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.