docs: create readmes for new kit flow

[nickolas-dimitrakas]

Background

• This PR starts a standardized README approach for kit directories so we have a consistent structure going forward

What Has Changed

• Added/updated README content to establish a reusable format for kit documentation.
• Defined the baseline structure we will follow for all future kits added to this repository.

Checklist

• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have tested this locally.

Reference Issue (For employees only. Ignore if you are an outside contributor)

• Closes https://go/j/938

[github-actions]

📦 SDK Size Impact Report

Measures how much the SDK adds to an app's size (with-SDK minus without-SDK).

Metric	Target Branch	This PR	Change
App Bundle Impact	1.66 MB	1.66 MB	+N/A
Executable Impact	896 bytes	896 bytes	+N/A
XCFramework Size	5.47 MB	5.47 MB	+N/A

➡️ SDK size impact change is minimal.

Raw measurements

Target branch (workstation/9.0-Release):

{"baseline_app_size_kb":84,"baseline_executable_size_bytes":75464,"with_sdk_app_size_kb":1788,"with_sdk_executable_size_bytes":76360,"sdk_impact_kb":1704,"sdk_executable_impact_bytes":896,"xcframework_size_kb":5604}

This PR:

{"baseline_app_size_kb":84,"baseline_executable_size_bytes":75464,"with_sdk_app_size_kb":1788,"with_sdk_executable_size_bytes":76360,"sdk_impact_kb":1704,"sdk_executable_impact_bytes":896,"xcframework_size_kb":5604}

[jamesnrokt]

Probably doesn't need to be said. Whether you're on the mono repo or the integrations site the install instructions are the same

[denischilik]

When partners integrate Kit with SMP they don't need to additionally set a dependency from mParticle it should be resolved automatically.