Fix /understanding/git links to use macro
Fix /understanding/git links to use macro

- Replace `(/understanding/git)` with `[u-git]` and `<@u_git/>`
- Edit `<@u_git/>` to render `/understanding/Git`
vizewang/sagan,dlizarra/sagan,dvaughn555/sagan,lowtalker/sagan,TabberGit/sagan,rwinch/sagan,seoilhyun/sagan,dharmaraju/sagan,dlizarra/sagan,dsyer/sagan,dsyer/sagan,andriykonoz/sagan,amit-siddhu/sagan,eonezhang/sagan,BHASKARSDEN277GITHUB/sagan,garylgh/sagan,yhj630520/sagan,seoilhyun/sagan,martinlippert/sagan,seoilhyun/sagan,dvaughn555/sagan,martinlippert/sagan,dkushner/sagan,mbateman/sagan,gregturn/sagan,eonezhang/sagan,dkushner/sagan,dsyer/sagan,dkushner/sagan,lowtalker/sagan,andriykonoz/sagan,mbateman/sagan,vizewang/sagan,eonezhang/sagan,dvaughn555/sagan,BHASKARSDEN277GITHUB/sagan,yhj630520/sagan,mbateman/sagan,TabberGit/sagan,dlizarra/sagan,amit-siddhu/sagan,andriykonoz/sagan,dharmaraju/sagan,martinlippert/sagan,dkushner/sagan,andriykonoz/sagan,rwinch/sagan,TabberGit/sagan,spring-io/sagan,martinlippert/sagan,rwinch/sagan,eonezhang/sagan,lowtalker/sagan,mbateman/sagan,yhj630520/sagan,spring-io/sagan,dharmaraju/sagan,yhj630520/sagan,dharmaraju/sagan,lowtalker/sagan,garylgh/sagan,vizewang/sagan,garylgh/sagan,TabberGit/sagan,dvaughn555/sagan,BHASKARSDEN277GITHUB/sagan,spring-io/sagan,dsyer/sagan,spring-io/sagan,amit-siddhu/sagan,garylgh/sagan,vizewang/sagan,amit-siddhu/sagan,BHASKARSDEN277GITHUB/sagan,dlizarra/sagan,gregturn/sagan,gregturn/sagan,rwinch/sagan,seoilhyun/sagan