$ git branch --edit-description
; opens editor, write something, save and exit
; or simply use
$ git config branch.master.description "description text"
$ git config branch.master.description
; shows description of branch master

$ git-branch-description
* master        this is master branch
one             this is simple branch for testing

$ npm install git-br -g

$ git config --global alias.br !git-br

$ git br
* master        this is master branch
one             this is simple branch for testing

; .bash_profile
; list git branches with their descriptions
function branches() {
    branch=""
    branches=`git branch --list`
    while read -r branch; do
    clean_branch_name=${branch//\*\ /}
    description=`git config branch.$clean_branch_name.description`
    printf "%-15s %s\n" "$branch" "$description"
    done <<< "$branches"
}