readme: added "Contributing" section
readme: fix database server connection error message
install: store redmine applications logs @ /var/log/redmine/redmine/
install: store redmine vhost logs @ /var/log/redmine/nginx/
install: store supervisor logs @ /var/log/redmine/supervisor/
install: setup a logrotation job for redmine-vhost logs
install: indentation fixes
dockerfile: added volume mount instruction for `/var/log/redmine`
changelog: updated
Merge branch 'logs-volume'

Closes #52
dockerfile: install openssh-client package

Closes #47
config: fix REDMINE_HTTPS_HSTS_MAXAGE config option #55
init: added SMTP_OPENSSL_VERIFY_MODE configuration option
readme: clean up the "Mail" section
install: create .subversion directory in the data volume

Closes #54
install: create .ssh directory in the data volume

Refer #54
install: create dotfiles directory

Refer #54
init: moved codeblock to create dotfiles
init: generate ssh keys for redmine user

Refer #54
install: move supervisord process to /var/log/redmine/supervisor/

Refer #52