Remove Doc/c-api/intro.rst from nitignore

Author: Aniketsy

Doc/tools/.nitignore

@@ -3,7 +3,6 @@
 # Keep lines sorted lexicographically to help avoid merge conflicts.
 
 Doc/c-api/init_config.rst
-Doc/c-api/intro.rst
 Doc/c-api/stable.rst
 Doc/library/ast.rst
 Doc/library/asyncio-extending.rst