Added modal.
Merge branch 'master' of https://github.com/fluent/fluentd-docs

# By Kazuki Ohta (2) and Masahiro Nakagawa (1)
# Via Kazuki Ohta
* 'master' of https://github.com/fluent/fluentd-docs:
  add description of process monitoring
  add monitoring agent description
  Update Windows support information