Doc: add missing dot in about_core.rst (#4686)

Author: garnerrobert

docs/source/about_core.rst

@@ -1,7 +1,7 @@
 PROJ is a generic coordinate transformation software that transforms geospatial
 coordinates from one coordinate reference system (CRS) to another. This
 includes cartographic projections as well as geodetic transformations. PROJ
-is released under the :ref:`X/MIT open source license <license>`
+is released under the :ref:`X/MIT open source license <license>`.
 
 PROJ includes :ref:`command line applications<apps>` for easy conversion of
 coordinates from text files or directly from user input. In addition to the
@@ -15,4 +15,4 @@ coordinates into projected coordinates using a number of different cartographic
 projections. Over the years, as the need has become apparent, support for datum
 shifts has slowly worked its way into PROJ as well. Today PROJ supports more
 than a hundred different map projections and can transform coordinates between
-datums using all but the most obscure geodetic techniques.
+datums using all but the most obscure geodetic techniques.