DOC: add a MAINTAINERS file

This one indicates who to CC when sending changes affecting certain
parts of the product.
diff --git a/.gitignore b/.gitignore
index acdbcc9..45ff1c3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -56,6 +56,7 @@
 !/Makefile
 !/README
 !/CONTRIBUTING
+!/MAINTAINERS
 !/ROADMAP
 !/SUBVERS
 !/VERDATE