Dependencies for `check-broken-links.sh` about developer

[vdice]

blc is added from its node_modules path in the script here: https://github.com/fermyon/developer/blob/main/.build/check-broken-links.sh#L40-L41

timeout is included in the gnu coreutils pkg which I think is usually present in most Linux distros and on my MacOS machine I've installed via brew install coreutils. Windows I am not sure 😅. This could also be an opportunity to devise a different approach that would cut out this dependency in the script...

[tpmccallum]

Apologies if I am missing something - I normally run the following procedure when performing local preview/testing:

# Go into spin-up-hub section
cd spin-up-hub/
# NPM install
npm install
# Go back into just developer folder
cd ../
# NPM install
npm install
# Build the site for local preview
spin build
# Bartholomew's linting
bart check content/the-file-to-check.md
# Run the node linting and tests
npm run test (this does the check for broken links with Spin actually running in the background)
# Local preview the site at localhost:3000
spin up -e "PREVIEW_MODE=1"

[ThorstenHans]

Installing coreutils on my mac did the trick. I'll add a note about that to the testing section of the contributing page in a dedicated PR