docs: fix readme code sample, docker tag, and navigation

[bezzad]

Documentation-only cleanup of README.md. No source code was touched.

Changes

• Table of Contents — added near the top, linking every top-level section plus the four "How to …" subsections, so the 860-line file is navigable.
• Quick Start — new section before Sample Console Application with one install command and a minimal DownloadBuilder example.
• Git Workflow consistency — the section told contributors to branch from and target vX.Y.Z in some places and develop in others. It now says develop everywhere (steps 5 and 10, and the closing paragraph).
• Code block language hints — tagged the ASCII .download file-layout diagram as text, and converted the two indented install snippets into fenced text / bash blocks. Every fenced block in the file now carries a language.
• Grammar and typos — fixed the '.downlaod' typo, a sentence fragment in the Content-Length section, "chunker downloads" → "chunk downloads", "please giving it a ⭐" → "please give it a ⭐", several "default values is" → "the default value is", and a few mid-sentence capitalizations in code comments. Meaning and tone are unchanged.

Items that were already correct

Two requested fixes turned out to be already fixed on develop, so this PR does not change them:

• The Authorization = new AuthenticationHeaderValue("Bearer", …) line in the Complex Configuration sample has no stray semicolon.
• The Docker command in Contributing already uses mcr.microsoft.com/dotnet/sdk:10.0.

Noted, not changed

The Building a Native AOT Version section still documents .NET 8.0 SDK and -f net8.0 publish commands. That is pre-existing content outside the scope of this cleanup, but it may be worth refreshing to net10.0 in a follow-up.

---

Generated by Claude Code

[bezzad]

CI red on continuous-integration/appveyor/branch, but the same check is failing on the base branch too, so it is not caused by this PR.

• develop @ 28b6fc0 — continuous-integration/appveyor/branch: failure (build 54437747)
• master @ 10ece6b — continuous-integration/appveyor/branch: failure (build 54404351)
• this PR @ 5cd4b4e — continuous-integration/appveyor/branch: failure (build 54437931)

This change only edits README.md — no source, no project files, no appveyor.yml — so it cannot affect a build or test outcome. The failing build also gives up roughly 40 seconds in, well before appveyor.yml finishes downloading the .NET 8/9/10 SDKs in its install: step, which points at an environment or configuration problem rather than a compile or test failure.

The AppVeyor build logs are not publicly readable (the API returns 403), so I could not confirm the underlying error. Worth noting that the base branches report under the AppVeyor project Behzadkhosravifar/downloader while this PR reports under Behzadkhosravifar/downloader-hkk6c — if that second project is a stale duplicate, its branch status may be misconfigured.

The GitHub Actions build (10.0.x) jobs, CodeFactor, and GitGuardian are the meaningful checks here; I will follow up if any of those fail. I will re-run against the base branch once it goes green.

---

Generated by Claude Code

[bezzad]

Follow-up: continuous-integration/appveyor/pr has now failed as well (build 54437933). Also pre-existing, and there is direct precedent for it.

PR #237 (develop-cf-autofix → develop, opened 9 July, unrelated to this change) shows the same split at its head commit e14388e:

• continuous-integration/appveyor/branch: success
• continuous-integration/appveyor/pr: failure

So the /pr build has been failing on this repository for PRs whose content has nothing to do with mine. Between then and now the /branch build has degraded too — it passed on #237 in July but fails today on both develop (28b6fc0) and master (10ece6b).

Both AppVeyor contexts are therefore red for reasons that predate this branch, on a commit that changes only README.md. Nothing here is fixable from the PR side; it needs someone with access to the AppVeyor project settings and build logs.

Everything else on 5cd4b4e is green so far — License Compliance (FOSSA), CodeFactor, and GitGuardian have all passed. The three GitHub Actions build (10.0.x) jobs are still running; I will report if any of them fail.

---

Generated by Claude Code