run PULPino on Ubuntu 20.04

[Ali77124]

I followed the instructions at https://youtu.be/kTVUJyRyibU but I got the following error when running hello:

$ make clean all run VERBOSE=1
Makefile:16: /tools/rules/pmsis_rules.mk: No such file or directory
make: *** There are no rules to make target "/tools/rules/pmsis_rules.mk". Stop.

I set the RULES_DIR path in the Makefile as follows:
$(pulp-sdk)/tools/rules/pmsis_rules.mk

Thanks for your tips.