Add build instructions to README (closes #9)

Document prerequisites (Go, protoc, golangci-lint, gofumpt), build
commands, and go install instructions.

README.md

@@ -52,6 +52,37 @@ Reading file contents and computing cryptographic hashes for manifest generation
 - **NO_COLOR:** Respect the `NO_COLOR` environment variable for disabling colored output.
 - **Options pattern:** Use `NewWithOptions(opts *Options)` constructor pattern for configurable types.
 
+# Building
+
+## Prerequisites
+
+- Go 1.21 or later
+- `protoc` (Protocol Buffers compiler) — only needed if modifying `.proto` files
+- `golangci-lint` — for linting (`go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest`)
+- `gofumpt` — for formatting (`go install mvdan.cc/gofumpt@latest`)
+
+## Build
+
+```sh
+# Build the binary
+make bin/mfer
+
+# Run tests
+make test
+
+# Format code
+make fmt
+
+# Lint
+make lint
+```
+
+## Install from source
+
+```sh
+go install sneak.berlin/go/mfer/cmd/mfer@latest
+```
+
 # Build Status
 
 [![Build Status](https://drone.datavi.be/api/badges/sneak/mfer/status.svg)](https://drone.datavi.be/sneak/mfer)