We are now using hash-based note file names instead of mkstemp() (cf.
commit 5c6a00ee93e54cc044aee5146e9fcfbcb732a2ee). Update the
documentation accordingly. Also, add a note on the garbage collector we
added in 8d71923d4f498c8d2fcb22a72346e3e77a7c4a5b.
Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>
6d88b330f2