linux-config: clean-up namespaces docs

[philips]

The docs don't reflect things we discussed in-person:

• Adding the path field
• Making the namespaces OS specific
• Plumbing through the hooks to make changes to the namespace

@crosbymichael volunteered for this one I think.

[mrunalp]

@philips I can take on the hooks portion of it (talked with @crosbymichael today and he told me look into it). I have assigned myself to #20

[philips]

@mrunalp Can you also document the restrictions on joining namespaces from a new user namespace that was discussed? I believe @LK4D4 had details and maybe even linux code/doc references we can use.

[mrunalp]

@philips Yes, sure. @LK4D4 and I discussed how a hook would have to be provided to allow customization of other namespaces from a user namespace. @LK4D4 could help review that :)

[philips]

@mrunalp Can you get a draft of your current thinking up sometime tomorrow?

[mrunalp]

There are PRs open for the first two items for Linux. I will put up a draft for the namespaces tomorrow.

[vbatts]

discussed during review.