remove yarn.lock; changed README.md to include npm install for client

[paulywill]

• I have read Chapter's contributing guidelines.
• My pull request has a descriptive title (not a vague title like Update README.md).
• My pull request targets the master branch of Chapter.

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Troubleshooting errors with docker-compose up on OSX (10.13.6)
someone in the Discord mentioned to resolve this you have to cd client && npm install

Added the missing instruction to the README.md

Instead of individual commands, I strung them together with &&.:

npm install && cd client && npm install && cd ..

Since quite of bit of the README kept indicating using npm install, I removed the yarn.lock file and instead included the package-lock.json

[pdotsani]

Maybe we can split this command into separate lines:

npm install
cd client
npm install // client packages (someone can give a better desc here...)

No need for the cd .. I think.

[pdotsani]

Just one note. Also, your yarn.lock and package-lock.json shouldn't be included in the pr unless you added dependencies.

[paulywill]

Ack'd

I'll close this PR and open a new one with just the README edit.