Add doc/faqs.md.

This is imported from the website; in the future the website
version will be drawn from here.

Added a FAQ on the use of `\AtEndPreamble` for cases when
the contents of `header-includes` need to refer to definitions
that come later in the preamble.  See #7422.

doc/faqs.md

@@ -0,0 +1,110 @@
+% FAQs
+
+::: faqs
+
+## How can I convert a whole directory of files from Markdown to RTF?
+
+On linux or OSX:
+
+    for f in *.txt; do pandoc "$f" -s -o "${f%.txt}.rtf"; done
+
+
+In Windows Powershell:
+
+    gci -r -i *.txt |foreach{$rtf=$_.directoryname+"\"+$_.basename+".rtf";pandoc -f markdown -s $_.name -o $rtf}
+
+## I used pandoc to convert a document to ICML (or OPML or RTF), and when I try to open it I'm told it's invalid.  What have I done wrong?
+
+Be sure to use the `-s` or `--standalone` flag, or you just get a
+fragment, not a full document with the required header:
+
+    pandoc -s -f markdown -t icml -o my.icml my.md
+
+## I get a blank document when I try to convert a markdown document in Chinese to PDF.
+
+By default, pandoc uses pdflatex to generate the PDF, and pdflatex
+doesn't handle Chinese characters. But you can change the default to
+use xelatex instead. You should also make sure you're using a font
+with Chinese glyphs.  For example:
+
+    pandoc -o c.pdf --pdf-engine=xelatex -V mainfont='Adobe Ming Std'
+
+## The Windows installer does a single user install, rather than installing pandoc for all users. How can I install pandoc for all users?
+
+Run the following command as admin:
+
+    msiexec /i pandoc-VERSION.msi ALLUSERS=1
+
+This will put pandoc in `C:\Program Files\Pandoc`.
+You can install Pandoc to a different directory by setting APPLICATIONFOLDER parameter,
+for example:
+
+    msiexec /i pandoc-1.11.1.msi ALLUSERS=1 APPLICATIONFOLDER="C:\Pandoc"
+
+## How do I change the margins in PDF output?
+
+The option
+
+    -V geometry:margin=1in
+
+will set the margins to one inch on each side.  If you don't want uniform
+margins, you can do something like
+
+    -V geometry:"top=2cm, bottom=1.5cm, left=1cm, right=1cm"
+
+Or
+
+    -V geometry:"left=3cm, width=10cm"
+
+For more options, see the documentation for the LaTeX [geometry
+package](https://www.ctan.org/pkg/geometry).
+
+## How does pandoc compare to multimarkdown?
+
+Here is a [wiki
+page](https://github.com/jgm/pandoc/wiki/Pandoc-vs-Multimarkdown)
+comparing the two.
+
+## When I specify an image width of 50% and convert to LaTeX, pandoc sets the height to textheight and the aspect ratio isn't preserved. How can I prevent this?
+
+For example, if you convert an image with `{width="50%"}`, the LaTeX produced
+will be `\includegraphics[width=0.5\textwidth,height=\textheight]`.
+
+This output presupposes the following code in pandoc's default latex
+template:
+
+```
+% Scale images if necessary, so that they will not overflow the page
+% margins by default, and it is still possible to overwrite the defaults
+% using explicit options in \includegraphics[width, height, ...]{}
+\setkeys{Gin}{width=\maxwidth,height=\maxheight,keepaspectratio}
+```
+
+If you don't have this in your custom template, you should
+add it.  If we didn't set the `height` explicitly in this way,
+the image would not be resized correctly unless it was
+being resized to smaller than its original size.
+
+## Pandoc sometimes uses too much memory. How can I limit the memory used by pandoc?
+
+`pandoc +RTS -M30m -RTS` will limit heap memory to 30MB.
+When converting a document requires more than this, an out of
+memory error will be issued.
+
+## When using `--include-in-header` with PDF or LaTeX output, how do I reference tex declarations coming after `$header-includes$` in the default template?
+
+For various reasons, the `$header-includes$` are not at the very
+end of the LaTeX preamble.  This poses a problem when the code
+you are inserting depends on declarations in the preamble coming
+after the `$header-includes$` location. For example, you might
+want to reference the `\author` and `\title` metadata values
+(set at the very bottom of the preamble) and present them in
+margins. In that case you can wrap your code in `etoolbox`'s
+`\AtEndPreamble`.  The technique is demonstrated in [this
+gist](https://gist.github.com/JohnLukeBentley/9dda6166b9ee5c4127afd2b8cd16b70a).
+When using `\AtEndPreamble`, keep any `makeatletter` or
+`makeatother` outside of the `\AtEndPreamble`, as shown in the
+example.
+
+:::
+