Before this change, this documentation in this repo would present the
reader with both U+0022 and U+201D quotation marks. The documentation
should always present U+0022 when it’s required for technical reasons
(i.e., bash commands). To be consistent, when U+0022 isn’t required,
the documentation should either

1. always present U+0022 QUOTATION MARKs at the beginning and end of
   quotations or
2. always present a U+201C LEFT DOUBLE QUOTATION MARK at the beginning
   and always present a U+201D RIGHT DOUBLE QUOTATION MARK at the end
   of quotations.

I chose option 2 because Unicode says that it’s preferred.[1]

The correct way to implement this choice (unfortunately) depends on
which file in this repo we’re looking at. For AsciiDoc, I decided to
use substitution. I could have included the Unicode characters directly,
but including characters that aren’t on most keyboards seems to go
against AsciiDoc’s philosophy. AsciiDoc is supposed to be easy to
write.[2] Plus, including non-ASCII characters in AsciiDoc just seems
wrong.

For Markdown, I just included the Unicode characters directly since
Markdown is meant to look good even before it’s been converted to
another format.[3]

Links:

1. https://www.unicode.org/charts/PDF/U0000.pdf#page=3
2. https://asciidoctor.org/docs/what-is-asciidoc/#the-zen-of-writing-asciidoc
3. https://daringfireball.net/projects/markdown/