docs: add Getting Started sections to root and project READMEs #63

[SakshiTamshetti]

Summary

Added "Getting Started" sections to the root README and all three project READMEs.

What was missing

The existing READMEs describe the high-level purpose well, but a developer
picking up this repo for the first time had no clear path from "I cloned it"
to "it ran." Specifically, there were no:

• .NET SDK version requirements or build prerequisites
• dotnet restore, dotnet build, or dotnet run commands
• Instructions for configuring the Kepware API base URL and credentials
• End-to-end example showing how to connect and list channels/devices

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What this PR adds

File	What was added
README.md	Quick-start routing table + one-liner for each project
Kepware.Api/README.md	Install, DI registration, credential config, list channels example
KepwareSync.Service/README.md	Clone, env vars table, appsettings.json, build, SyncToDisk, agent mode
Kepware.Api.Sample/README.md	Clone, credential setup, build/run, expected output, troubleshooting table

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What was NOT changed

• No existing content was removed or restructured
• No code files were touched
• All additions are documentation only

---

Checklist

• Confirmed none of this information existed in the READMEs before this PR
• All commands tested against .NET SDK 8.0
• Credential security guidance included (env vars over hard-coded passwords)
• Windows PowerShell and Linux/macOS snippets both provided
• All option names match the existing CLI reference in the repo exactly

[SakshiTamshetti]

Hi @rlabbeptc ,

As discussed in the issue, I've added Getting Started sections to:

• README.md (root)
• Kepware.Api/README.md
• KepwareSync.Service/README.md
• Kepware.Api.Sample/README.md

Each section adds only what was confirmed missing:

• .NET SDK 8.0 prerequisite + dotnet restore/build/run commands
• Credential config via environment variables and appsettings.json
• End-to-end example listing channels and devices

No existing content was removed or changed.