docs: add pnpm to list of tools needed in getting started doc

[flippingbitss]

As a new contributor, I was following the Getting Started doc and running just init failed due to pnpm not installed. So, added pnpm to the list in development.md. (this is my first PR, 😺 )

Running just init

INFO Installing binaries...
 INFO Installing binaries...
 INFO Installing binaries...
 INFO Installing binaries...
 INFO Installing binaries...
 INFO Done in 1.964751222s
# Node.js related init
pnpm install
bash: line 1: pnpm: command not found
error: Recipe `init` failed on line 21 with exit code 127

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[connorshea]

I ran into the same problem! :)