Add Go link to three posts

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Author: alexellis

_posts/2019-02-14-serverless-single-page-app.md

@@ -217,6 +217,8 @@ Each function is automatically secured with HTTPS to encrypt traffic.
 
 ### Read the code
 
+> OpenFaaS is written in Go. Checkout my new book [Everyday Go](https://gumroad.com/l/everyday-golang) for practical tips and hands-on examples to gain experience quickly or to level-up.
+
 You can find the code for all three functions in the following GitHub repo. Fork or star the repo and share with your network.
 
 * [alexellis/leaderboard-app](https://github.com/alexellis/leaderboard-app)

_posts/2019-04-10-golang-serverless.md

@@ -357,6 +357,8 @@ OpenFaaS provides a flexible templating system and build process through the use
 
 You can learn how to deploy OpenFaaS to Kubernetes and build functions and microservices using the [OpenFaaS workshop](https://github.com/openfaas/workshop/).
 
+> OpenFaaS is written in Go. Checkout my new book [Everyday Go](https://gumroad.com/l/everyday-golang) for practical tips and hands-on examples to gain experience quickly or to level-up.
+
 ### Join the community
 
 The OpenFaaS community values are: developers-first, operational simplicity, and community-centric.

_posts/2021-01-31-gitea-faas.md

@@ -176,6 +176,8 @@ Once logged in, we will create a git repository so when we need to add webhooks
 
 For this guide we will be using golang for the Gitea bot, but you can use any language that you are comfortable working with.
 
+> OpenFaaS and Gitea are both written in Go. Checkout Alex's new book [Everyday Go](https://gumroad.com/l/everyday-golang) for practical tips and hands-on examples to gain experience quickly or to level-up.
+
 To get started, we'll need to pull the prebuilt OpenFaaS template, and create the skeleton of a function using `faas-cli`.
 
 ```bash