Addtional docs

[peter-lawrey]

This documentation-centric pull request adds a formal requirements specification for Java Thread Affinity, dramatically expands the README into a full user guide, and refreshes JavaDocs.
There are no functional or behavioural changes to the library—only whitespace in one helper class.

Area	File(s)	Summary of changes
New spec	affinity/src/main/adoc/requirements.adoc	• 300-line AsciiDoc Requirements Document covering scope, functional & NFRs, architecture, APIs, native code, build & test strategy.
User guide	README.adoc (+ ≈120 / -4 LOC)	• Added Supported operating systems section. • Detailed install instructions for JNA on Windows. • Explained -Daffinity.reserved masks with worked examples. • How to set isolcpus via GRUB & systemd-boot. • Descriptions of AffinityStrategies, dumpLocks() output, lock-file directory, and AffinityThreadFactory.
JavaDocs	ITicker.java	• Re-written header explaining tick semantics and helper methods.
Cosmetics	LinuxHelper.java	• Re-indentation (tabs → spaces) of sched_setaffinity; no logic change.

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Motivation

• Provide newcomers with a single, authoritative requirements spec.
• Make platform capabilities and configuration steps clear in the README.
• Improve code readability via richer JavaDocs.