docs: add preliminary version of the Merkle DAG diagram

docs/data-model.rst

@@ -3,6 +3,14 @@
 Data model
 ==========
 
+.. _swh-merkle-dag:
+.. figure:: images/swh-merkle-dag.svg
+   :width: 1024px
+   :align: center
+
+   Software Heritage archive as a Merkle DAG, augmented with crawling
+   information (click to zoom).
+
 TODO
 
 Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor

docs/images/.gitignore

+swh-merkle-dag.pdf
+swh-merkle-dag.svg

docs/images/Makefile

+
+MERKLE_DAG = swh-merkle-dag.svg
+
+BUILD_TARGETS =
+BUILD_TARGETS += $(MERKLE_DAG)
+
+all: $(BUILD_TARGETS)
+
+
+# dia exporters
+
+%.eps: %.dia
+	dia -t eps --export $@ $<
+
+%.svg: %.dia
+	dia -t svg --export $@ $<
+
+# generic converters
+
+%.pdf: %.eps
+	epstopdf $<
+
+
+clean:
+	-rm -f $(BUILD_TARGETS)