bug: remove patch-package postinstall script breaking npm installs

[thescientist13]

Related Issue

#233

Summary of Changes

1. Remove patch-package postinstall script that was breaking npm installs in feature(plugins): support wcc signals in import jsx plugin greenwood#1667
2. Document manual running of patch-package in CONTRIBUTING.md

---

The failure is due to WCC having a postinstall script to run patch-package but as it is only a dev dep, it won't be found and will fail. (and honestly, we really shouldn't be shipping with a postinstall script)

warning Workspaces can only be enabled in private projects.
[4/4] Building fresh packages...
error /home/runner/work/greenwood/greenwood/node_modules/wc-compiler: Command failed.
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
Exit code: 127
Command: patch-package
Arguments: 
Directory: /home/runner/work/greenwood/greenwood/node_modules/wc-compiler
Output:
/bin/sh: 1: patch-package: not found
Error: Process completed with exit code 127.