package missing files from cmake directory

Author: isuruf

MANIFEST.in

@@ -1,3 +1,3 @@
 include CMakeLists.txt LICENSE README.md symengine_version.txt
 recursive-include symengine *.cpp *.h *.hpp CMakeLists.txt *.in *.cmake *.pyx *.pxd *.py *.pxi
-recursive-include cmake *.cpp *.in *.cmake *.pyx
+recursive-include cmake *.cpp *.in *.cmake *.pyx *.py *.txt