add reasoning for security zones

[lilachic]

Describe the pull request:

• Bug fix
• Functional change
• New feature
• Code cleanup
• Build system change
• [ x ] Documentation change
• Language translation

Pull request long description:

Add content to document section Local security / zone considerations

Changes made:

Related issues:

Additional information:

Release note:

Documentation change:

Mentions:

[blankdots]

I am fine with this level of description, though might be good to get other opinions to see if we need to go into depth with diagrams of anything else

[pontus]

Looks good, added some language suggestions, feel free to disregard them if you prefer.

[lilachic]

If no more changes is asked this is ready to be merged.

Just do notice, anyone did not comment about "- Differences in deployment make concrete examples challenges, explain what can be exemplified and what not in this guide" line at the beginning, I kept it as guideline and forgot to remove.

Now I changed it to be more aligned with rest of the text "Differences in deployment make concrete examples challenging, here it is explained only the guidelines."