Removed yarn as a package manager

[chase-west]

We shouldn't be using two package managers, it can lead to errors such as:

Module not found: Package path ./generated is not exported from package C:\Users\chase\OneDrive\Desktop\opensource\website\node_modules\contentlayer (see exports field in C:\Users\chase\OneDrive\Desktop\opensource\website\node_modules\contentlayer\package.json)
4 | import { useEffect, useState } from 'react'
5 | import ProjectCard from '../../components/ProjectCard'
6 | import { allProjects, allFunds } from 'contentlayer/generated'
7 | import { Project, Fund } from 'contentlayer/generated'
8 |
9 | const AllProjects: NextPage<{ projects: Project[]; funds: Fund[] }> = ({
10 |Import trace for requested module:
11 |./pages/index.tsx

I've removed yarn because installing packages with npm instead resolved this error (and likely prevents future ones).

Changes in README.md:

• Updated the command to install dependencies from yarn to npm install.
• Updated the command to run the local development version from yarn dev to npm run dev.

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