teracyhq-incubator#28 | add doc how to install kubectl - helm

docs/how-to-install-upgrade-downgrade-kubectl-helm.md

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+This page shows you how to install, upgrade and downgrade kubectl and helm on macOS, Linux (Ubuntu) and Windows via the packages:
+
+- Homebrew on macOS
+- Snap on Linux (Ubuntu)
+- Chocolatey on Windows
+
+# Requirements:
+
+- homebrew available on macOS
+- chocolatey available on Windows
+- Ubuntu is preferred Linux distro
+
+
+# Installing, upgrading and downgrading kubectl on your computer
+``kubectl`` is the Kubernetes command line tool, which can be used to deploy settings to the cluster.
+In this section, you should know how to install, upgrade and downgrade a version of kubectl. 
+
+## Installing kubectl
+
+With the guide below, the latest version of kubeclt should be installed.
+
+
+
+- On macOS, follow the official documentation at https://kubernetes.io/docs/tasks/tools/install-kubectl/#install-with-homebrew-on-macos.
+
+- On Linux (Ubuntu), follow the official documentation at https://kubernetes.io/docs/tasks/tools/install-kubectl/#install-with-snap-on-ubuntu.
+
+- On Windows, follow the official documentation at https://kubernetes.io/docs/tasks/tools/install-kubectl/#install-with-chocolatey-on-windows.
+
+Note: On Windows, to install kubectl with the autocompletion, you should add the option `-y` at the end of the command.
+
+```
+choco install kubernetes-cli -y
+```
+
+## Upgrading kubectl
+This section shows you how to upgrade the latest verion of kubeclt.
+
+- On macOs:
+
+```
+brew upgrade kubernetes-cli
+```
+
+- On Linux (Ubuntu):
+
+//TODO
+
+- On Window, use the command:
+
+```
+choco upgrade kubernetes-cli -y
+```
+
+
+## Downgrading kubectl 
+
+This section shows you how to install an older version of kubectl, e.g `verion 1.11`, use the command below:
+
+- On macOs: See the details at https://www.benpickles.com/articles/72-downgrading-kubectl-with-homebrew
+
+- On Linux (Ubuntu):
+
+//TODO
+
+- On Windows:
+
+```
+$ choco install kubernetes-cli --version 1.11 -y --allow-downgrade
+```
+
+# Installing, upgrading and downgrading helm on your computer
+
+Helm is a package management tool for Kubernetes, and is used to deploy charts. In this section, you should know how to install, upgrade and downgrade helm.
+
+## Installing helm
+
+To install the latest version of helm on different OS, please see this official document https://docs.helm.sh/using_helm/#installing-the-helm-client.
+
+Note: To install helm with the autocompletion, you should add the option `-y` at the end of the command.
+For example, install the helm on Windows:
+
+```
+choco install kubernetes-helm -y
+```
+## Upgrading helm
+
+- On macOs:
+
+```
+brew upgrade kubernetes-helm
+```
+
+- On Linux (Ubuntu):
+
+//TODO
+
+- On Windows:
+
+```
+choco upgrade kubernetes-helm -y
+```
+
+
+## Downgrading helm
+You can install an older verion of helm, e.g `verion 2.10.0`, use the command below:
+
+- On macOs: 
+
+You can switch to an installed verion, for example, version 2.9.1
+
+```
+$ brew switch kubernetes-helm 2.9.1```
+```
+
+Or install a specific version by following the steps below, to have more details, see https://github.com/helm/helm/issues/4547#issuecomment-423312200.
+	- Click https://github.com/Homebrew/homebrew-core/search?q=kubernetes-helm&type=Commits to search for the correct `kubernetes-helm.rb` file for the version, for example, v2.9.1.
+	- Click the commit hash button (78d6425)
+	- Click the "View" button
+	- Click the "Raw" button
+	- Copy the url: https://raw.githubusercontent.com/Homebrew/homebrew-core/78d64252f30a12b6f4b3ce29686ab5e262eea812/Formula/kubernetes-helm.rb
+	- Run the commands below:
+
+	```
+	$ brew unlink kubernetes-helm
+	$ brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/78d64252f30a12b6f4b3ce29686ab5e262eea812/Formula/kubernetes-helm.rb
+	$ brew switch kubernetes-helm 2.9.1
+	```
+
+- On Linux (Ubuntu):
+
+//TODO
+
+- On Windows:
+
+```
+$ choco install kubernetes-helm --version 2.10.0 -y --allow-downgrade
+```