boot-time labs: add blank spreadsheet to help with tests

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>

labs/boot-time-software-measurement/boot-time-software-measurement.tex

@@ -128,24 +128,12 @@ \section{Timing the launching of the application}
 
 \section{Initial measurements}
 
-Now, take your calculator and fill the below table with the results from your experiments:
-
-\begin{tabular}{| l | l | r |}
-  \hline
-  Step & Duration & Description \\
-  \hline
-  \hline
-  U-Boot SPL & & Between \code{U-Boot SPL 2022.04} and \code{U-Boot 2022.04} \\
-  \hline
-  U-Boot & & Between \code{U-Boot 2022.04} and \code{Starting kernel} \\
-  \hline
-  Kernel & & Between \code{Starting kernel} and \code{Run /sbin/init} \\
-  \hline
-  Init scripts & & Between \code{Run /sbin/init} and \code{Starting ffmpeg} \\
-  \hline
-  Application & & Between \code{Starting ffmpeg} and \code{First frame decoded} \\
-  \hline
-  \hline
-  Total & & \\
-  \hline
-\end{tabular}
+Now, run the test 3 times and using LibreOffice Calc, fill the \code{Run 1},
+\code{Run 2} and \code{Run 3} columns in the table in the
+\code{~/boot-time-labs/results/initial.ods} spreadsheet. The averages and standard
+deviations of the measurements will be computed automatically.
+
+Here's the kind of results you should get after filling the table:
+
+\includegraphics[width=\textwidth]{labs/boot-time-software-measurement/initial.png}
+