docs: update installation to use cargo install ccsync

Simplified installation to single command now that crates are
properly named for crates.io publishing:

Before:
  cargo install --path crates/ccsync-cli

After:
  cargo install ccsync

Removed build from source instructions - users can find that
in CONTRIBUTING.md if needed.

Author: onsails

README.md

@@ -7,14 +7,7 @@ Keep your Claude Code setup consistent across projects while maintaining project
 ## Installation
 
 ```bash
-cargo install --path crates/ccsync-cli
-```
-
-Or build from source:
-
-```bash
-cargo build --release
-# Binary available at: target/release/ccsync
+cargo install ccsync
 ```
 
 ## Quick Start