Add documentation draft for PodRemediator (behaviour, POC, and troubleshooting)

Description:

Add a first draft of user-facing and operator-facing documentation for PodRemediator. The draft should cover: what PodRemediator is and when it triggers remediation; the dependency on NHC and SNR; supported storage scenarios (e.g. local PVs, LVMS, node affinity); configuration options of the PodRemediator CR (e.g. namespaces, EnablePVCRemediation); alignment with operator expectations for stateful workloads (e.g. Galera, RabbitMQ) regarding storage recovery and rescheduling; how to run the POC (reference to the runbook and high-level steps); and basic troubleshooting (e.g. controller not Ready, NHC/SNR missing, PVC not deleted, node not NotReady). The deliverable can be a new doc file (e.g. in docs/) or a section in an existing doc; it may be refined later for release notes and formal docs approval.

Acceptance criteria:

• A documentation draft exists (e.g. in docs/) describing PodRemediator's purpose, behaviour, and when it triggers remediation.
• The draft documents the NHC/SNR dependency, supported storage scenarios, and CR configuration options.
• The draft references the POC runbook and outlines the main steps to run the POC.
• A basic troubleshooting section covers at least: controller not Ready, NHC/SNR not installed, PVC not deleted after node failure, and node not reported as NotReady.
• The draft is reviewable (e.g. Markdown in the repo); it may be marked as draft or WIP until docs approval.