docs: adjust install section

[filipsobol]

Rollup Plugin Name: swc

This PR contains:

• [ ] bugfix
• [ ] feature
• [ ] refactor
• [X] documentation
• [ ] other

Are tests included?

• [ ] yes (bugfixes and features will not be merged without tests)
• [X] no

Breaking Changes?

• [ ] yes (breaking changes will not be merged unless absolutely necessary)
• [X] no

Description

The @swc/core package is a peer dependency of @rollup/plugin-swc, so it may need to be installed separately depending on your package manager. Npm 7+ automatically installs peer dependencies, but older versions and other package managers don't (at least not by default).

[tada5hi]

duplicate of #1666