xls-workshop-openlane: add diy section

[proppy]

• add diy section for people to work on their own design

TEST=https://colab.research.google.com/github/proppy/silicon-notebooks/blob/workshop-diy/xls-workshop-openlane.ipynb TEST=https://colab.research.google.com/github/proppy/silicon-notebooks/blob/workshop-diy/xls-workshop-openlane-ja.ipynb

@shige-compit @t-sasatani do you think we need something like this?

[t-sasatani]

I think it'll be better to have that (although we can probably ask re-using or copying the multiplier code blocks)

[proppy]

@t-sasatani what would be the Japanese equivalent? 自由研究?

[t-sasatani]

I think just English is ok for that part because there's no real equivalent word (also 自由研究 makes me feel like I need to submit a report!)

[proppy]

rebased and added japanese equivalent.

[proppy]

@shige-compit reviewed offline and suggested the rewording