Update material

[jhirvioja]

• Should not conflict with https://github.com/kubernetes-hy/kubernetes-hy.github.io/pull/150
• Fixed typos
• Added Knative link
• Removed "Kubernetes Up and Running" resource links, as they were dead and no "official" sources have it available for download. The book can be found via Google, but they are (unofficial) 3rd party sources which can't be trusted for security reasons.
• Updated kubectl completion part to be a bit more clear
• Removed StorageOS resource link, it no longer exists (someone bough it out)
• Updated one example command from deprecated version to new one
• kubectl get po -> kubectl get pods; nit/nothing inherently wrong about this, shorthand for the command is just not explained at any point in the material, makes it a bit more consistent
• pod_for_debugging.yaml gets italicized in the material due to snake case for. removing underscores fixes this (all other .yaml files are also not snakecased, so a bit more consistent)

[jhirvioja]

Continued in https://github.com/kubernetes-hy/kubernetes-hy.github.io/pull/159

[jhirvioja]

good but kubectl po should not be changed

Reverted 👍