\documentclass[MYTHESISMAIN.tex]{subfiles}

\begin{document}

%==============================================================================
\chapter{Useful information}%
\label{sec:app}
%==============================================================================

In the appendix you usually include extra information that should be
documented in your thesis, but not interrupt the flow.

The \LaTeX\ WikiBook~\cite{latexwiki} is a useful source of information on \LaTeX.

\end{document}
