docs: Polish README for the initial Hex release

[zacky1972]

Summary

• Polishes README.md for the initial Hex v0.1.0 release.
• Replaces conditional installation wording with release-oriented Hex dependency instructions.
• Adds canonical Hex package / HexDocs links and states that they become live after publishing.
• Documents user prerequisites for Elixir/OTP and Docker.
• Adds a minimal runtime-configuration quick start and a Docker runtime example using the actual v0.1.0 public API.
• Separates v0.1.0 released preview functionality from future LSP client roadmap work.
• Fixes README formatting by using fenced code blocks and proper Markdown tables.

Notes

Only README.md is changed. The final ## License section in README.md is preserved byte-for-byte by the apply script.

The apply script verifies that the branch includes the latest origin/main when a Git origin remote is available, then checks for the release-scope, Hex metadata, and changelog readiness markers that issue #46 builds on.

Validation

Run from the repository root:

bash /path/to/issue-46-readme-polish-apply.sh
mix format --check-formatted
mix docs
mix check

The apply script also validates that:

• the latest-main readiness docs and metadata markers are present before applying;
• the README ## License section is unchanged after applying;
• fenced code blocks are balanced;
• old roadmap / conditional installation wording is gone; and
• git diff --check -- README.md passes when run inside a Git worktree.