docs(doclicense): Add sections: What license to use and REUSE spec

Related to: #72

doclicense/doclicense.dtx

@@ -136,7 +136,7 @@ corresponds to \PackageName\nobreakspace\fileversion, dated \printdateTeX{\filed
 % \changes{2.2.0}{2020/09/18}{Add Japanese and Bulgarian translation. Add hint how to use Chinese to docs. Load hyperxmp by default when it is installed. Before, doclicense just suggested to load it and made use of the package when the user did.}
 % \changes{2.2.1}{2020/09/25}{Fix compatibility issue with newer versions of hyperxmp (bug confirmed with Tex Live 2020) resulting in an compile error by loading hyperxmp and hyperref in the order the packages expect it.}
 % \changes{2.3.0}{2021/03/13}{Add option to disable the use of hyperxmp and add compatibility for pdfx. Use \url{https://reuse.software/} for the doclicense source code itself.}
-% \changes{2.4.0}{2021/XX/XX}{Add Croatian translation. Update Spanish translation to match Creative Commons website. Add note to README that CC license texts and images are licensed themselves under CC0-1.0.} % Add a short note to CTAN maintainers when uploading: "Please consider the changed license statement in README.md"
+% \changes{2.4.0}{2021/XX/XX}{Add Croatian translation. Add sections about choosing a license and the REUSE specification. Update Spanish translation to match Creative Commons website. Add note to README that CC license texts and images are licensed themselves under CC0-1.0.} % Add a short note to CTAN maintainers when uploading: "Please consider the changed license statement in README.md"
 %
 %
 
@@ -515,6 +515,32 @@ corresponds to \PackageName\nobreakspace\fileversion, dated \printdateTeX{\filed
 % \end{eqlist}
 % \makeatother
 %
+% \section{What license to choose for the document?}
+%
+% The list of available licenses is long (see
+% \href{https://spdx.org/licenses/}{SPDX License List}). Only a (small) subset
+% of them are a good choice for documentation. The \doclicenseLongType family
+% seem to be a common choice as contributions to this package have shown. This
+% package was translated to 15+ languages but no other license families have
+% been added yet. With that, a link to
+% \href{https://creativecommons.org/choose/}{Creative Commons: Choose a
+% License} is probably justified if you have not done that already.
+%
+% \section{REUSE Specification}
+%
+% That clarifies the question under which license you want to put the document
+% under, but in practice it might not be as easy as that.
+% Under what license are the artifacts (images/figures/tables/source code
+% listings) you are including? It would probably be useful to track such
+% metadata along with the files. For this, the \href{REUSE
+% Specification}{https://reuse.software/} can be used.
+%
+% The REUSE Specification is independed of \LaTeXe{} and more \enquote{low
+% level} than this package.
+% \PackageName{} might integrate with the REUSE Specification at a later point.
+% Refer to \url{https://github.com/ypid/latex-packages/issues/72} for
+% discussion how such an integration could look like.
+%
 % \section{Contributing}
 % \label{sec:contributing}
 % This package is being developed on GitHub: \url{\PackageURL}. When you want