Update merge_requests.md with a simpler way to check out a merge request
Update merge_requests.md with a simpler way to check out a merge request

The previous way was put under the
"By modifying `.git/config` for a given repository" section. The
disadvantage is that one has to modify `.git/config` for each repository
that one uses. The new way was put under the "By adding a git alias"
section. One has to create this git alias once, and then it will work
from any repository, without having to modify `.git/config` over and
over again.
htve/GitlabForChinese,openwide-java/gitlabhq,LUMC/gitlabhq,stoplightio/gitlabhq,LUMC/gitlabhq,dplarson/gitlabhq,LUMC/gitlabhq,stoplightio/gitlabhq,openwide-java/gitlabhq,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,mr-dxdy/gitlabhq,darkrasid/gitlabhq,iiet/iiet-git,shinexiao/gitlabhq,htve/GitlabForChinese,icedwater/gitlabhq,mr-dxdy/gitlabhq,mmkassem/gitlabhq,darkrasid/gitlabhq,daiyu/gitlab-zh,shinexiao/gitlabhq,jirutka/gitlabhq,iiet/iiet-git,jirutka/gitlabhq,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,screenpages/gitlabhq,SVArago/gitlabhq,SVArago/gitlabhq,icedwater/gitlabhq,mr-dxdy/gitlabhq,openwide-java/gitlabhq,t-zuehlsdorff/gitlabhq,openwide-java/gitlabhq,jirutka/gitlabhq,mr-dxdy/gitlabhq,stoplightio/gitlabhq,allysonbarros/gitlabhq,axilleas/gitlabhq,daiyu/gitlab-zh,darkrasid/gitlabhq,daiyu/gitlab-zh,darkrasid/gitlabhq,LUMC/gitlabhq,jirutka/gitlabhq,shinexiao/gitlabhq,htve/GitlabForChinese,screenpages/gitlabhq,dplarson/gitlabhq,icedwater/gitlabhq,axilleas/gitlabhq,dreampet/gitlab,dplarson/gitlabhq,htve/GitlabForChinese,dplarson/gitlabhq,dreampet/gitlab,dreampet/gitlab,daiyu/gitlab-zh,dreampet/gitlab,SVArago/gitlabhq,icedwater/gitlabhq,axilleas/gitlabhq,allysonbarros/gitlabhq,allysonbarros/gitlabhq,allysonbarros/gitlabhq,screenpages/gitlabhq,iiet/iiet-git,iiet/iiet-git,axilleas/gitlabhq,t-zuehlsdorff/gitlabhq,shinexiao/gitlabhq,stoplightio/gitlabhq,screenpages/gitlabhq,SVArago/gitlabhq