docs: add two plugins pkg and sh

[JounQin]

prettier-plugin-pkg for package.json
prettier-plugin-sh for shell scripts

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory)
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/pr-XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

✨Try the playground for this PR✨

[fisker]

I think we should add some descriptions to these plugins. I mean all plugins.

@thorn0 @evilebottnawi

[thorn0]

@fisker Agree. This list probably needs to be turned into a table.

[kachkaev]

Should the plugins be inserted so that the list remained alphabetical?

[lipis]

Yes I agree that we have to turn this thing into a table.. but in a separate PR..

Some suggestions for the columns:

• Name
• Description
• AST (if it's changing the AST or not)
• Additional options
• (Anything else?)