Update sections.md
Update sections.md

Add Android build system intro section
dlizarra/sagan,yhj630520/sagan,seoilhyun/sagan,dsyer/sagan,rwinch/sagan,rwinch/sagan,dharmaraju/sagan,TabberGit/sagan,rwinch/sagan,gregturn/sagan,andriykonoz/sagan,dkushner/sagan,dharmaraju/sagan,dvaughn555/sagan,BHASKARSDEN277GITHUB/sagan,BHASKARSDEN277GITHUB/sagan,dvaughn555/sagan,eonezhang/sagan,garylgh/sagan,dlizarra/sagan,mbateman/sagan,vizewang/sagan,martinlippert/sagan,martinlippert/sagan,lowtalker/sagan,eonezhang/sagan,amit-siddhu/sagan,yhj630520/sagan,spring-io/sagan,TabberGit/sagan,amit-siddhu/sagan,martinlippert/sagan,gregturn/sagan,seoilhyun/sagan,martinlippert/sagan,dvaughn555/sagan,dvaughn555/sagan,eonezhang/sagan,lowtalker/sagan,mbateman/sagan,spring-io/sagan,dkushner/sagan,mbateman/sagan,amit-siddhu/sagan,lowtalker/sagan,BHASKARSDEN277GITHUB/sagan,mbateman/sagan,dsyer/sagan,seoilhyun/sagan,vizewang/sagan,rwinch/sagan,spring-io/sagan,vizewang/sagan,dharmaraju/sagan,andriykonoz/sagan,yhj630520/sagan,gregturn/sagan,dkushner/sagan,seoilhyun/sagan,amit-siddhu/sagan,dlizarra/sagan,eonezhang/sagan,garylgh/sagan,vizewang/sagan,yhj630520/sagan,spring-io/sagan,lowtalker/sagan,garylgh/sagan,garylgh/sagan,andriykonoz/sagan,dsyer/sagan,dlizarra/sagan,dsyer/sagan,BHASKARSDEN277GITHUB/sagan,andriykonoz/sagan,TabberGit/sagan,dharmaraju/sagan,TabberGit/sagan,dkushner/sagan