docs(getting-started): add installation guide

Author: dndungu

content/docs/getting-started/installation.md

@@ -0,0 +1,114 @@
+---
+title: Installation
+weight: 1
+bookToc: true
+---
+
+# Installation
+
+Zerfoo requires **Go 1.25 or later**. [Download Go](https://go.dev/dl/) if you haven't already.
+
+Verify your Go installation:
+
+```bash
+go version
+# go version go1.25.0 linux/amd64
+```
+
+## As a Library
+
+Add Zerfoo to your Go module:
+
+```bash
+go get github.com/zerfoo/zerfoo@latest
+```
+
+Then import it in your code:
+
+```go
+import "github.com/zerfoo/zerfoo"
+```
+
+For just tensors and GPU compute, import `github.com/zerfoo/ztensor`. For just tokenization, import `github.com/zerfoo/ztoken`.
+
+## CLI
+
+Install the `zerfoo` command-line tool:
+
+```bash
+go install github.com/zerfoo/zerfoo/cmd/zerfoo@latest
+```
+
+This places the `zerfoo` binary in your `$GOPATH/bin` (or `$HOME/go/bin` by default). Make sure this directory is in your `PATH`.
+
+## Build from Source
+
+```bash
+git clone https://github.com/zerfoo/zerfoo.git
+cd zerfoo
+go build -o zerfoo ./cmd/zerfoo
+```
+
+Zerfoo builds with **zero CGo by default** (`CGO_ENABLED=0`). GPU acceleration is loaded dynamically at runtime via purego/dlopen, so you do not need CUDA headers, shared libraries, or build tags to compile. A plain `go build` produces a fully static binary.
+
+## Platform Support
+
+Zerfoo compiles on any platform supported by Go 1.25, including **Linux**, **macOS**, and **Windows**.
+
+GPU acceleration is available on:
+
+| Backend | Hardware | Platforms |
+|---------|----------|-----------|
+| CUDA | NVIDIA GPUs | Linux, Windows |
+| ROCm | AMD GPUs | Linux |
+| OpenCL | Cross-vendor | Linux, macOS |
+
+For GPU setup instructions, see [GPU Setup](/docs/architecture/gpu-setup/).
+
+## Verify Installation
+
+### Library
+
+Create a test file to confirm the library is importable:
+
+```bash
+mkdir zerfoo-test && cd zerfoo-test
+go mod init zerfoo-test
+go get github.com/zerfoo/zerfoo@latest
+```
+
+```go
+package main
+
+import (
+	"fmt"
+	"github.com/zerfoo/zerfoo"
+)
+
+func main() {
+	fmt.Println("zerfoo imported successfully")
+	_ = zerfoo.Load
+}
+```
+
+```bash
+go run main.go
+# zerfoo imported successfully
+```
+
+### CLI
+
+```bash
+zerfoo version
+```
+
+This prints the installed version. If the command is not found, ensure `$GOPATH/bin` is in your `PATH`:
+
+```bash
+export PATH="$PATH:$(go env GOPATH)/bin"
+```
+
+## Next Steps
+
+- [Quickstart](/docs/getting-started/quickstart/) -- pull a model and run your first inference
+- [GPU Setup](/docs/architecture/gpu-setup/) -- configure CUDA, ROCm, or OpenCL for hardware-accelerated inference