You can either download the source using the "ZIP" button at the top of the github page, or you can make a clone using git:
git clone https://github.com/croncat/memento.git
$ make
# make install
For help, type 'memento' in your terminal.
memento 0.1a [alpha] ( http://github.com/croncat/memento )
Usage: memento [OPTION] {ARGUMENT/S}
OPTIONS:
-l: list all categories
-a: add category
-d: delete category
-n: add new note/message to category
-s: show all notes/messages in category
-r: remove note/message from category
EXAMPLES:
memento -l
memento -a netlog
memento -d commands
memento -n quotes "my first quote, yeah!"
memento -s films
memento -r quotes 151
memento: fast and minimalist note-taking application