Update custom_hooks.md for global custom hooks and chained hook info
Update custom_hooks.md for global custom hooks and chained hook info

https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/93

dplarson/gitlabhq,openwide-java/gitlabhq,dplarson/gitlabhq,dreampet/gitlab,t-zuehlsdorff/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,dreampet/gitlab,htve/GitlabForChinese,stoplightio/gitlabhq,htve/GitlabForChinese,jirutka/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,axilleas/gitlabhq,openwide-java/gitlabhq,axilleas/gitlabhq,jirutka/gitlabhq,iiet/iiet-git,LUMC/gitlabhq,jirutka/gitlabhq,axilleas/gitlabhq,iiet/iiet-git,darkrasid/gitlabhq,darkrasid/gitlabhq,openwide-java/gitlabhq,darkrasid/gitlabhq,LUMC/gitlabhq,t-zuehlsdorff/gitlabhq,dplarson/gitlabhq,dplarson/gitlabhq,mmkassem/gitlabhq,darkrasid/gitlabhq,jirutka/gitlabhq,htve/GitlabForChinese,LUMC/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,openwide-java/gitlabhq,LUMC/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,t-zuehlsdorff/gitlabhq,dreampet/gitlab,htve/GitlabForChinese,t-zuehlsdorff/gitlabhq,axilleas/gitlabhq