docs: memory limit kind note

[tr0njavolta]

Description of your changes

Adds note to user to update their Docker memory limit to 16gb

Fixes #

I have:

• Read and followed Modelplane's contribution process.
• Run nix flake check (or ./nix.sh flake check) and made sure it passes.
• Added or updated tests covering any composition function changes.
• Signed off every commit with git commit -s.

[negz]

Do we know we need 16GB? Would e.g. 12GB be enough? If someone has a 16GB laptop I don't think they could allocate 16GB to kind.

I ran the getting started guide through to installing the IG and found that needs ~9GB. It would be useful to test how much memory is needed for the most resource intensive stage of the guide (e.g. multiple ICs running).

[negz]

Thanks @tr0njavolta!