Add some FIXMEs for problematic wording.

Author: zygoloid

source/utilities.tex

@@ -19956,6 +19956,7 @@
 The \fmtgrammarterm{type} determines how the data should be presented.
 
 \pnum
+% FIXME: What is a "string" here, exactly?
 The available string presentation types are specified in \tref{format.type.string}.
 %
 \begin{floattable}{Meaning of \fmtgrammarterm{type} options for strings}{format.type.string}{ll}
@@ -19967,6 +19968,8 @@
 \end{floattable}
 
 \pnum
+% FIXME: What about void* and nullptr_t?
+% FIXME: What about strings? Do they get padding for alignment?
 Formatting of objects of arithmetic types and \tcode{const void*}
 is done as if by calling \tcode{to_chars} (unless otherwise specified)
 and copying the output through the output iterator of the format context