Improve documentation

[0x2b3bfa0]

Old issue snippets preserved for documentation purposes:

https://github.com/datachain-ai/platform/issues/2501

I made up a weird hybrid between the documentation and iterative/helm-charts@dc56bf6/README.md in real time during [a customer] call. 🙈

Consolidated version

$ helm repo update iterative
$ helm upgrade --install --atomic --namespace studio --values values.yaml studio iterative/studio 

[!NOTE]
I believe helm repo add iterative https://helm.iterative.ai shouldn't be necessary, but it looked like they didn't have the repository locally. 🤯

https://github.com/datachain-ai/platform/issues/1881

Studio Self-hosted: Document Git repo updates not reflected in Studio on dvc.org
Webhook troubleshooting

https://github.com/datachain-ai/platform/issues/1362

One customer experienced a rare issue where the K3s node was marked NotReady.

Running kubectl uncordon <node> fixed the problem.

We need to add this to the troubleshooting section on dvc.org