git: add git usage

Signed-off-by: Micky Ching <mickyching@gmail.com>
move index.html to index

Signed-off-by: Micky Ching <mickyching@gmail.com>
move C++ to clang

Signed-off-by: Micky Ching <mickyching@gmail.com>
add C notes

Signed-off-by: Micky Ching <mickyching@gmail.com>
emacs: add keys

Signed-off-by: Micky Ching <mickyching@gmail.com>
emacs: add org notes

Signed-off-by: Micky Ching <mickyching@gmail.com>
python: add notes

Signed-off-by: Micky Ching <mickyching@gmail.com>