How to capitalize Xcode, Git, git, and HEAD

Xcode has always been “Xcode” with a capital “X” and a lower-case “c”. Here's the press release dated June 23, 2003 announcing the first release of Xcode. Here's a video of Steve Jobs introducing Xcode 1.0 at WWDC 2003, and it says “Xcode” on the slide. (Youtube took down the video.)

“Git”, when referring to the system, is a proper noun and is therefore, by English language convention, spelled “Git” with a capital “G”. Example sentence from the Git User Manual:

It will be useful to have a Git repository to experiment with as you read this manual.

The command-line program that provides access to the system is “git” with a lower-case “g”, because all-lowercase is the historic convention for Unix commands. If your filesystem is case-insensitive (which is the default on OS X), you can sometimes get away with capitalizing some or all of its letters, but it's a bad idea to make that a habit.

The currently-checked out commit in Git is spelled “HEAD” in all capitals, because that string is embedded in the git source code in many places. Example:

if (resolve_gitlink_ref(submodule, "HEAD", oid.hash) == 0)

You can sometimes get away with not capitalizing some or all of the letters if your filesystem is case-insensitive (which is the default on OS X), but it's a bad idea to make that a habit.

To illustrate that Git would never be spelled GIT, consider Git 2.28 (Q3 2020) and its doc updates.

See commit 788db14 (07 Jun 2020) by Denton Liu (Denton-L).
^{(Merged by Junio C Hamano -- gitster -- in commit 653a351, 18 Jun 2020)}

t/README: avoid poor-man's small caps GIT

^{Signed-off-by: Denton Liu}

In 48a8c26c62 ("Documentation: avoid poor-man's small caps GIT", 2013-01-21, Git v1.8.2-rc0 -- merge), the documentation was amended to spell Git's name as Git when talking about the system as a whole.
However, t/README was skipped over when the treatment was applied.

Bring t/README into conformance with the CodingGuidelines by casing "Git" properly.

While we're at it, fix a small typo. Change "the git internal" to "the Git internals".

"git" is reserved for commands. Git for the product. GIT for... nobody.