Update README and skill install guidance

Author: linhay

.skills/swift-git/SKILL.md

@@ -69,6 +69,17 @@ Examples (do not auto-run)
 - "Run a single test": use `swift test --filter <TestName>` as shown above.
 - "Check package manifest": open Package.swift at repository root.
 
+Installation (SwiftPM)
+- Base library:
+  - Product: `SwiftGit`
+- Optional embedded git bundles (manual opt-in):
+  - Arm64 bundle product: `SwiftGitArm64`
+  - X86_64 bundle product: `SwiftGitX86_64`
+  - Universal bundle product: `SwiftGitUniversal`
+- Usage pattern (prefer embedded, fallback to system):
+  - `Git(environments: [.embed(.arm64), .system])`
+  - Replace `.arm64` with `.x86_64` or `.universal` when using the corresponding product.
+
 Packaging the skill
 - To package this skill (manual step), follow your environment's packaging script. Example: `scripts/package_skill.py swift-git.skill` (if package exists in your environment).
 

README.md

@@ -100,14 +100,13 @@ Embedded git bundle
 - `SwiftGit` (base product) no longer embeds a bundle; `.embed(.arm64/.x86_64/.universal)` works only when the corresponding resource product is linked.
 - `GitEnvironment.Style.auto` now maps to system git only; use `.embed(...)` explicitly when you add a resource product.
 
-Example usage (arm64):
+Example usage (arm64, prefer embedded then system fallback):
 
 ```swift
 import SwiftGit
-import SwiftGitResourcesArm64
+import SwiftGitArm64
 
-let env = try GitEnvironment(type: .embed(.arm64))
-let git = Git(environment: env)
+let git = Git(environments: [.embed(.arm64), .system])
 ```
 - Agents and tests should not modify files under the bundles. Use `GitEnvironment.Style.custom(URL)` to point to an alternate git distribution.
 - To generate updated bundles, run `tools/update-git-bundle.sh` with the desired `--archs` and copy the result into the corresponding `Sources/SwiftGitResources*/Resource/` directory.