Added example snippets of the presentation.

Dockerfile

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+FROM r-base:4.1.2
+
+# Install several CRAN packages using package manager.
+RUN apt update \
+    && apt install --assume-yes \
+    r-cran-dplyr=1.0.7-2 \
+    r-bioc-deseq2=1.34.0+dfsg-1 \
+    r-cran-biocmanager=1.30.16+dfsg-3 \
+    r-cran-devtools=2.4.3-1
+
+# Example how to install specific package using R.
+RUN R -e "BiocManager::install('apeglm', dependencies=TRUE, version='3.14')"
+
+# Make a directory in the Docker image and copy scripts to it.
+WORKDIR /analysis/
+COPY ./example/ /analysis/
+
+# Run unit tests.
+CMD R --quiet -e 'testthat::test_dir("test")'