Added instructions for installing kn (#2045)

Author: abrennan89

docs/install/install-kn.md

@@ -0,0 +1,26 @@
+---
+title: "Installing the `kn` Client"
+linkTitle: "Installing the `kn` Client"
+weight: 10
+type: "docs"
+---
+
+## Install `kn` using the nightly executable binary
+To install the `kn` Client, you must download the executable binary for your system. Links to the latest nightly executable binary are available here:
+  - [macOS](https://storage.googleapis.com/knative-nightly/client/latest/kn-darwin-amd64)
+  - [Linux](https://storage.googleapis.com/knative-nightly/client/latest/kn-linux-amd64)
+  - [Windows](https://storage.googleapis.com/knative-nightly/client/latest/kn-windows-amd64.exe)
+
+You must place the executable binary in your system path, and make sure that it is executable.
+
+## Install `kn` using Go
+1. Check out the [Client repository](https://github.com/knative/client).
+1. Run the command:
+  ```
+  go install ./cmd/kn
+  ```
+
+## `kn` container images
+The `kn` container images are available here:
+- [Nightly container image](gcr.io/knative-nightly/knative.dev/client/cmd/kn)
+- [Latest release](gcr.io/knative-releases/knative.dev/client/cmd/kn)