README file rebuild instructions missing package

[Roland Haas]

The current instructions in Baikal to regenerate code say

pip install sympy==1.11
git clone https://github.com/zachetienne/nrpytutorial.git
cd nrpytutorial
git checkout b60bba29582ae563aaae5340638674ce8ddc2c79
cd BaikalETK
make

which, when done in a virtualenv (to actually control sympy version) fails due to missing ipython. One should should thus install both sympy and ipython

python3 -m venv $PWD
source bin/activate
pip install sympy==1.11 ipython
git clone https://github.com/zachetienne/nrpytutorial.git
cd nrpytutorial
git checkout b60bba29582ae563aaae5340638674ce8ddc2c79
cd BaikalETK
make

‌

[Roland Haas]

Switched over to use pip in git hash 3697431 "Baikal*: update to current nrpy master; update README" of wvuthorns