Write is as a macro, name it Notes.
Code:
/echo This is a note I am writing to myself.


You can put it on a hotbar and bam, instant reminder as when you click it you'll get "This is a note I am writing to myself" right there in chat!
If you set it to macro #0 you can even include the command to open your macro list and edit it any time as it'll be the first one open.

Code:
/macros
/echo This is a note I am writing to myself
/echo It's pretty neat!