Add text about copyleft and GPL. Remove \centering.

free-sw-rh-interns.tex

@@ -79,6 +79,17 @@
   say it is \textbf{non-free}.
 \end{frame}
 
+\begin{frame}{What's Free Software?$^3$}
+  The \textbf{copyleft} concept was the smartest hack that Stallman
+  has created.  It exploits how the copyright works, and turns it back
+  against itself.
+  \newline
+  \newline
+  The \textbf{GNU General Public License}, or \textbf{GPL}, is the
+  tool with which we guarantee that the software freedom will
+  be respected by everyone.
+\end{frame}
+
 \section{The G from GNU}
 \begin{frame}{The \texttt{G} from \texttt{GNU}}
   \begin{itemize}
@@ -100,7 +111,6 @@
 \end{frame}
 
 \begin{frame}{The \texttt{G} from \texttt{GNU}$^2$}
-  \centering
   But of course, we are not in a contest.  I choose to call the system
   \textbf{GNU/Linux} not only because I think it is the right thing to
   do, but mainly to \textbf{raise awareness}.
@@ -122,7 +132,6 @@
 
 \section{All that goes upstream...}
 \begin{frame}{All that goes upstream...}
-  \centering
   \textbf{Upstream} is the name we give to the actual Free Software
   projects that develop the programs.  For example, Linux,
   LibreOffice, GIMP, GDB, GTK.
@@ -163,7 +172,6 @@
 \end{frame}
 
 \begin{frame}{All that goes upstream...$^4$}
-  \centering
   The so-called \textbf{forges} are very popular nowadays.
   \textbf{GitHub} and \textbf{GitLab} are widely used; they provide an
   integrated bug tracking system, but don't provide a mailing list
@@ -182,7 +190,6 @@
 
 \section{... Must come downstream}
 \begin{frame}{... Must come downstream}
-  \centering
   \textbf{Downstream} is the name we give to the projects that
   \emph{package} the upstream projects.  For example, Fedora, RHEL,
   Debian, Ubuntu.  We also call them \textbf{distributions} (or