Update "Making your first figure" tutorial (#1997)

Co-authored-by: Dongdong Tian <[email protected]>

Author: michaelgrund

examples/get-started/first_figure.py

@@ -91,16 +91,19 @@
 # Set the projection
 # ------------------
 #
-# This figure now has its colors set, but there is no projection or size
-# set for the map. Both of these values are set using the ``projection``
-# parameter.
+# This figure now has its colors set. By default the projection and size
+# of the map is set to ``"Q15c+du"``. Here, ``"Q"`` defines a
+# cylindrical equidistant map projection, ``"15c+du"`` means setting
+# the maximum (upper) map dimension to 15 cm. However, both of
+# these values can be customized according to the requirements using
+# the ``projection`` parameter.
 #
 # The appropriate projection varies for the type of map. The available
 # projections are explained in the :doc:`projection </projections/index>`
 # gallery. For this example, the Mercator projection is set using ``"M"``.
-# The width of the figure will be 10 centimeters, as set by ``"10c"``. The map
-# size can also be set in inches using "i" (e.g. a 5 inch wide Mercator
-# projection would use ``"M5i"``).
+# The width of the figure will be 10 centimeters, as set by ``"10c"``.
+# The map size can also be set in inches using "i" (e.g. a 5 inch wide
+# Mercator projection would use ``"M5i"``).
 
 fig = pygmt.Figure()
 fig.coast(