docs/post launch docs feedback and clarifications

[thescientist13]

Related Issue

N / A

Summary of Changes

1. Added proper mini Table of Contents for Plugins and Content as data landing sections
2. Make custom imports usage script more generic (for example, the current location recommended does not work for pnpm)
3. Make custom imports script less generic to account for different package managers
4. Make Prerendering requirement of using a default export clearer for Scripts section
5. Document pnpm special instructions for shamefully-hoist option

TODO

1. Looks like I missed a patch that causes certain table of contents cases to render one less heading than there should be and now a heading is missing on the Plugins section page - table of contents sometimes missing first heading tag greenwood#1305
   
2. validate more generic custom imports loader location

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