move notes.txt to internal to avoid confusing people

internal/notes.txt

@@ -0,0 +1,10 @@
+- battery: when state or icon change, update with _p9k_set_prompt. make sure icons can be sent with
+  `typset -p` in zsh 5.1.
+- ram: reduce precision to 2 digits. check if it makes sense for all segments that use the same
+  function.
+- to avoid resetting prompt too often (e.g., when battery remaining time changes by 1 minute), can
+  do the following: send the current state from master to worker; worker sends new state if it's
+  different but it only triggers prompt reset if it's sufficiently different. this requires
+  disabling implicit reset on every eval in _p9k_worker_receive.
+- implement fake gitstatus api on top of vcs_info (or plain git?) + worker and use it if there is no
+  gitstatus.