Update install instructions (#29)

README.md

@@ -15,14 +15,16 @@ NOTE: Astro is currently experimental.
 
 **Installation**
 
-Install Astro using go get (Go >1.11 required):
+Install Astro using go get (Go >1.12 required):
 
 ```
-go get -u github.com/uber/astro/astro/cli/astro
+GO111MODULE=on go get github.com/uber/astro/astro/cli/astro
 ```
 
 This will install a binary called `astro` in your `$GOPATH/bin`.
 
+Alternatively, you can download precompiled binaries from the [Github releases page](https://github.com/uber/astro/releases).
+
 **Configuration**
 
 Astro looks for a configuration file called `astro.yaml` in the current or parent directories. It is recommended to place this file in the same top-level directory of your project where the Terraform code exists (e.g. `terraform/astro.yaml`).