Adds version command and Makefile for build info

Provides a `gitlocal version` command to display the application's version, commit hash, and build date.

Introduces a `Makefile` to automate builds, installations, and tests. The Makefile dynamically extracts version, commit, and date from git tags, commit hashes, and build timestamps, injecting this metadata into the Go binary via `ldflags`.

Updates the `README.md` to document the new command and recommended build process using the Makefile.

Makefile

@@ -0,0 +1,43 @@
+.PHONY: build install test clean version
+
+# Get version from git tag, fallback to dev
+VERSION ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo "dev")
+COMMIT ?= $(shell git rev-parse --short HEAD 2>/dev/null || echo "unknown")
+DATE ?= $(shell date -u +"%Y-%m-%dT%H:%M:%SZ")
+
+# Ldflags to inject version information
+LDFLAGS := -ldflags "-X git.membo.co.uk/dtomlinson/gitlocal/cmd.Version=$(VERSION) \
+                      -X git.membo.co.uk/dtomlinson/gitlocal/cmd.Commit=$(COMMIT) \
+                      -X git.membo.co.uk/dtomlinson/gitlocal/cmd.Date=$(DATE)"
+
+# Build the binary
+build:
+	@echo "Building gitlocal $(VERSION)..."
+	go build $(LDFLAGS) -o gitlocal .
+
+# Install to $GOPATH/bin
+install:
+	@echo "Installing gitlocal $(VERSION)..."
+	go install $(LDFLAGS) .
+
+# Run tests
+test:
+	@echo "Running tests..."
+	go test -v ./...
+
+# Run tests with coverage
+coverage:
+	@echo "Running tests with coverage..."
+	go test -coverprofile=coverage.out ./...
+	go tool cover -func=coverage.out
+
+# Clean build artifacts
+clean:
+	@echo "Cleaning..."
+	rm -f gitlocal coverage.out
+
+# Show version that would be built
+version:
+	@echo "Version: $(VERSION)"
+	@echo "Commit:  $(COMMIT)"
+	@echo "Date:    $(DATE)"