Add size/disk usage benchmarks

[alexkreidler]

According to the website, one of the major features is pnpm's minimal disk usage. If it is possible, could you add sizes of the folders (with du -sh or something) to the benchmark, so we could see for ourselves?

[brycekahle]

The size is actually in the results, just not graphed. See https://github.com/pnpm/node-package-manager-benchmark/blob/d87db894c1ebc3b7edbccf6f73591f5730574483/results/pnpm/1.9.0/react-app.yaml#L6 for example.

[zkochan]

That's true, but the disk space efficiency of pnpm will be visible only if running pnpm install in several projects that use the same store. However, currently, we have a separate store for each benchmark

[luxlogica]

This is particularly relevant now when comparing with Yarn 2 (issue #31). Yarn 2 compresses the installed packages by a lot, but we still get duplication - in order to support 'zero install', in Yarn 2 each project has its own cache folder with the compressed dependencies inside it.

Specially in large projects, this is likely to mean that over time, pnpm might still provide some advantage is saving disk space. But this does makes it more difficult to estimate it: you'd have to estimate how many times a package would have to be (re)installed in its compressed format by Yarn 2, compared to a single, uncompressed installation in the pnpm store.