RFR: Misc fixes

[Iris Clark]

On Thu, 23 Dec 2021 02:14:50 GMT, Jesper Wilhelmsson <jwilhelm at openjdk.org> wrote:

> - Changes casing in headers to be consistent
> - Fixed typos and minor cleanups
> - Changes all JTReg to jtreg since that's how it's written in the official documentation
> - Minor clarification in how to fix an incorrect backport

Marked as reviewed by iris (Reviewer).

src/index.md line 1467:

> 1465: This document assumes familiarity with the first two chapters of the free on-line book [Mercurial: The Definitive Guide](http://hgbook.red-bean.com).
> 1466: 
> 1467: ## Installing and configuring mercurial

I think you may want to capitalize "Mercurial" as that's the name of a tool.  They seem to follow this convention in their documentation.  Regardless of what you decide, I think the case on this line should match with the one on new line 1505 "Cloning a Mercurial repository" and other similar subtitles.

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PR: https://git.openjdk.java.net/guide/pull/71