Styleguide changes and crosslinks

[dtKinger]

WIP, not ready for review yet Ready to merge

• [x] Welcome to Knokd
• [x] Realtor Cooperation Policy
• [x] Getting Started
• [x] Listings
• [x] Saved Searches
• [x] Contacts

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 8d2fa56):

https://knokd-docs-30d6e--pr15-styleguide-changes-a-0su0hd3f.web.app

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[dtKinger]

Got a 👍 from Andrew in slack for this PR. Sorry it's a bit monolithic, but it contains sweeping changes for writing style, as well as content upgrades throughout. Some examples of things updated:

• The writing style in numbered lists
• Clarified instances of Log in (verb), Login (noun), Signup (deprecated for Sign-up), Sign-up (noun), Sign up (verb)
• Concept introductions edited for clarity
• Settled cases where interchangeable terms used ambiguously
• New documentation for "work area" and "exclusivity"
• URLs updated to follow the app, e.g. followers => contacts
• Small typos here and there