docs(create): explain sv add in generated README

[erenbati]

Closes #1328

Description

Adds an Adding features section to generated app and library READMEs so users discover sv add after project creation. It shows the interactive command and a Tailwind CSS example.

The generated README snapshots are updated and an sv patch changeset is included.

Validation

Local validation could not run because this environment could not resolve github.com while cloning the branch. Opening as draft so CI can validate the generated snapshots and repository checks.

Checklist

• Update snapshots (if applicable)
• Add a changeset (if applicable)
• Allow maintainers to edit this PR
• I care about what I'm doing, no matter the tool I use (Notepad, Sublime, VSCode, AI...)

[pkg-svelte-dev]

Install the latest version of sv from 2b042fa:

pnx https://pkg.svelte.dev/sv/c/2b042fa1816f448aeb939fa6a36b99c5504933a1 create

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/cli/pr/1338

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2b042fa

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
sv	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR