[stable/sysdig] Add 'How to upgrade to last version' to the README (#18403)

Signed-off-by: Federico Barcelona <fede_rico_94@hotmail.com>

stable/sysdig/CHANGELOG.md

@@ -3,6 +3,10 @@
 This file documents all notable changes to Sysdig Helm Chart. The release
 numbering uses [semantic versioning](http://semver.org).
 
+## v1.4.21
+
+* Add 'How to upgrade to last version' to the README
+
 ## v1.4.20
 
 ### Minor changes

stable/sysdig/Chart.yaml

@@ -1,6 +1,6 @@
 apiVersion: v1
 name: sysdig
-version: 1.4.20
+version: 1.4.21
 appVersion: 0.92.3
 description: Sysdig Monitor and Secure agent
 keywords:

stable/sysdig/README.md

@@ -177,6 +177,38 @@ And then, upgrade Helm chart with:
 $ helm upgrade my-release -f values.yaml stable/sysdig
 ```
 
+## How to upgrade to the last version
+
+First of all ensure you have the lastest chart version
+
+```bash
+$ helm repo update
+```
+
+In case you deployed the chart with a values.yaml file, you just need to modify (or add if it's missing) the `image.tag` field and execute:
+
+```bash
+$ helm install --name sysdig -f values.yaml stable/sysdig
+```
+
+If you deployed the chart setting the values as CLI parameters, like for example:
+
+```bash
+$ helm install \
+    --name sysdig \
+    --set sysdig.accessKey=xxxx \
+    --set secure.enabled=true \
+    --set ebpf.enabled=true \
+    --namespace sysdig-agent \
+    stable/sysdig
+```
+
+You will need to execute:
+
+```bash
+$ helm upgrade --set image.tag=<last_version> --reuse-values sysdig stable/sysdig
+```
+
 ## Adding custom AppChecks
 
 [Application checks](https://sysdigdocs.atlassian.net/wiki/spaces/Monitor/pages/204767363/) are integrations that allow the Sysdig agent to collect metrics exposed by specific services. Sysdig has several built-in AppChecks, but sometimes you might need to [create your own](https://sysdigdocs.atlassian.net/wiki/spaces/Monitor/pages/204767436/).