Add CLI install instruction and script

install/README.md

@@ -0,0 +1,37 @@
+# TK CLI Installation
+
+Binaries for macOS and Linux AMD64 are available for download on the 
+[release page](https://github.com/fluxcd/toolkit/releases).
+
+To install the latest release run:
+
+```bash
+curl -s https://raw.githubusercontent.com/fluxcd/toolkit/master/install/tk.sh | sudo bash
+```
+
+The install script does the following:
+* attempts to detect your OS
+* downloads and unpacks the release tar file in a temporary directory
+* copies the tk binary to `/usr/local/bin`
+* removes the temporary directory
+
+## Build from source
+
+Clone the repository:
+
+```bash
+git clone https://github.com/fluxcd/toolkit
+cd toolkit
+```
+
+Build the tk binary (requires go >= 1.14):
+
+```bash
+make build
+```
+
+Run the binary:
+
+```bash
+./bin/tk -h
+```