What are the two notes that Miranda finds and why are they so unsettling for Miranda?

Miranda finds two notes from an unknown source. One note is in her home, suggesting someone used the hidden spare key to plant the note in the apartment. The second warns Miranda not to talk to anyone about these notes and to write a story that contains information that has not yet happened. This note is confusing and a little frightening to Miranda. It also hints about foreknowledge, again touching on the theme of time travel.