Put project status in the README

Fixes https://github.com/ncmpcpp/ncmpcpp/issues/607.

README.md

@@ -2,6 +2,16 @@
 
 ## ncmpcpp – featureful ncurses based MPD client inspired by ncmpc
 
+### Project status
+
+The project is officially in maintenance mode. I (Andrzej Rybczak) still use it
+daily, but it's feature complete for me and there is very limited time I have
+for tending to the issue tracker and open pull requests.
+
+No new, substantial features should be expected (at least from me). However, if
+there are any serious bugs or the project outright stops compiling because of
+new, incompatible versions of dependencies, it will be fixed.
+
 ### Main features:
 * tag editor
 * playlist editor