[Nimok15]

Added a "How it works" section describing the PDK layer and the generator layer, and why that matters. Added a Requirements table and improved the installation guide. Added a table of the existing notebooks showing which PDK each one uses. Also explained the two backends: gdsfactory and gdstk.

[DonaldLucy]

Thanks for the update. I tried the new examples and found a few things that could further be inproved:

• GDS generation works with gdstk, but the next step, pdk.drc(top, "drc_out/"), fails with TypeError: Component.write_gds() got an unexpected keyword argument 'gdsdir'. Could you show a working DRC path for this backend, or note the current limitation?
• pip install . installs the KLayout Python package, but pdk.drc() also needs the separate klayout command on PATH. The requirements table should say so.
• The README says rules are read from the installed PDK at build time. The current SKY130 and GF180 rules are stored as numeric values in the repository, so kind of overclaiming. Maybe try to revise this.
• The setup check reports both PDKs as available even with an invalid PDK_ROOT, and the Troubleshooting link has no target.
  I reproduced the DRC errors. The GDS generation examples themselves worked with gdstk.