[otbn,doc] Fix capitalised Sim.py in diagram

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/hw/ip/otbn/doc/dv/model.svg b/hw/ip/otbn/doc/dv/model.svg
index d258423..9f7018b 100644
--- a/hw/ip/otbn/doc/dv/model.svg
+++ b/hw/ip/otbn/doc/dv/model.svg
@@ -611,7 +611,7 @@
          x="630"
          y="191.60423"
          style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-family:'Liberation Sans';-inkscape-font-specification:'Liberation Sans'"
-         id="tspan2265">directory, Sim.py forms the core of the instruction</tspan><tspan
+         id="tspan2265">directory, sim.py forms the core of the instruction</tspan><tspan
          sodipodi:role="line"
          x="630"
          y="213.20847"