Fix sp_kill README docs to match proc behavior

[BrentOzar]

Summary

Addresses Copilot review feedback from #3885 (sp_kill docs only — sp_BlitzLock feedback will be handled separately):

• @RequestsOlderThanMinutes → @RequestsOlderThanSeconds: The example used a parameter name that doesn't exist in the proc. Fixed to @RequestsOlderThanSeconds = 300.
• @SPIDState default: Docs said "empty string for both" but the proc validates NULL/S/R and raises an error on empty string. Fixed to "NULL for both (default)".
• @ExecuteKills safety claim: Docs said a targeting filter is required with @ExecuteKills = 'Y', but the proc doesn't enforce that — it kills all non-system sessions when no filters are specified. Updated wording to accurately describe the behavior as a warning rather than a false constraint.

Test plan

• Verify README parameter names match sp_kill.sql parameter declarations
• Verify example code runs without error against the proc signature

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Updates sp_kill documentation in README.md to accurately reflect the stored procedure’s current parameter names, defaults/validation rules, and behavior when @ExecuteKills = 'Y'.

Changes:

• Corrects the example parameter name to @RequestsOlderThanSeconds (with 300 seconds shown for 5 minutes).
• Fixes @SPIDState default documentation to NULL (since empty string is invalid per proc validation).
• Rewords @ExecuteKills = 'Y' guidance to warn that running without filters can kill broadly, rather than claiming a filter is enforced.

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[Copilot]

The wording “all non-system sessions are killed” is a bit too absolute: sp_kill excludes the caller’s own session (s.session_id <> @OurSessionID) and never recommends/kills sessions in rollback status. Consider adjusting this sentence to match the proc’s actual eligibility rules (e.g., user sessions with session_id > 50, excluding your own and rollbacks) to avoid an apparent contradiction with the Safety features section below.

Suggested change

	* @ExecuteKills = 'Y' or 'N' (default 'N') - whether to actually kill, or just show recommendations. When set to 'Y' with no targeting filters, all non-system sessions are killed - so always specify at least one filter to avoid killing everything.
	* @ExecuteKills = 'Y' or 'N' (default 'N') - whether to actually kill, or just show recommendations. When set to 'Y' with no targeting filters, sp_kill can kill broadly across eligible user sessions (for example, user sessions with session_id > 50), excluding your own session and sessions already in rollback - so always specify at least one filter to avoid killing nearly everything.