Revise README for improved clarity and structure

Brings ai-authorship note above the fold, and adds a note about imperfect isolation guarantee.

Signed-off-by: bdeshi <bdeshi@bdeshi.space>

README.md

@@ -1,14 +1,20 @@
 ![shannoncoat — which coat will Claude wear today?](docs/hero.png)
 
-Run multiple isolated Claude profiles on macOS — each one its own Claude Desktop
-**and** its own paired Claude Code setup — and tell their windows apart at a
-glance.
+Run multiple isolated [**\***](#isolation) Claude profiles on macOS — each one
+its own Claude Desktop **and** its own paired Claude Code setup — and tell their
+windows apart at a glance.
 
-Your normal Claude install is left completely alone. It stays exactly as it is
-and keeps working normally; shannoncoat only adds profiles alongside it.
+Your normal Claude install is left alone. It stays as it is and keeps working
+normally; shannoncoat only adds profiles alongside it.
 
 A menu-bar item allows quick switching and profile management.
 
+---
+> [!NOTE]
+> shannoncoat started as the shell script in the first commit, written by hand.
+Claude built the GUI app out of it — most of the Swift, the icon, and this
+README — working from human direction, review, and dogfooding.
+
 ## Requirements
 
 - macOS 13 or later
@@ -115,8 +121,12 @@ rather than killing Claude underneath it. Answer the dialog.
 
 ## Build from source
 
-Requires the Xcode Command Line Tools.
+Local builds require the Xcode Command Line Tools.
+```
+xcode-select --install
+```
 
+Then run the build script
 ```bash
 ./build.sh
 ```
@@ -129,8 +139,12 @@ every time, which silently invalidates its Accessibility grant on each rebuild.
 `.env.example` walks through creating a self-signed certificate once so the
 permission survives.
 
----
+## Isolation
 
-shannoncoat started as the shell script in the first commit, written by hand.
-Claude Code built the app out of it — most of the Swift, the icon, and this
-README — working from direction, review and testing.
+> [!IMPORTANT]
+> Perfect isolation is not guaranteed. Claude and Claude Code can have functionally
+> full disk access regardless of which profile it's running from, including access
+> to default configuration folders.
+> 
+> Some Claude integrations — skills, plugins, etc — may also hardcode the
+> `~/.claude` path which may modify content in there.