feat: update to use core tap for gastown installation (#872)

Signed-off-by: Rui Chen <rui@chenrui.dev>

.goreleaser.yml

@@ -164,7 +164,7 @@ release:
 
     **Homebrew (macOS/Linux):**
     ```bash
-    brew install steveyegge/gastown/gt
+    brew install gastown
     ```
 
     **npm (Node.js):**

README.md

@@ -97,9 +97,10 @@ Git-backed issue tracking system that stores work state as structured data.
 
 ```bash
 # Install Gas Town
-go install github.com/steveyegge/gastown/cmd/gt@latest
+$ brew install gastown                                    # Homebrew
+$ go install github.com/steveyegge/gastown/cmd/gt@latest  # From source
 
-# Add Go binaries to PATH (add to ~/.zshrc or ~/.bashrc)
+# If using go install, add Go binaries to PATH (add to ~/.zshrc or ~/.bashrc)
 export PATH="$PATH:$HOME/go/bin"
 
 # Create workspace with git initialization