Update SUPPORTED_BROWSERS.md
Update SUPPORTED_BROWSERS.md

Add title header and downgrade others to sub-titles.
phillips1021/uPortal,jhelmer-unicon/uPortal,jhelmer-unicon/uPortal,groybal/uPortal,stalele/uPortal,bjagg/uPortal,groybal/uPortal,jhelmer-unicon/uPortal,stalele/uPortal,jonathanmtran/uPortal,ChristianMurphy/uPortal,GIP-RECIA/esco-portail,jonathanmtran/uPortal,jhelmer-unicon/uPortal,GIP-RECIA/esup-uportal,stalele/uPortal,apetro/uPortal,phillips1021/uPortal,apetro/uPortal,jhelmer-unicon/uPortal,groybal/uPortal,stalele/uPortal,Jasig/uPortal,stalele/uPortal,jl1955/uPortal5,jl1955/uPortal5,phillips1021/uPortal,phillips1021/uPortal,phillips1021/uPortal,jl1955/uPortal5,Jasig/uPortal,jl1955/uPortal5,ChristianMurphy/uPortal,apetro/uPortal,ChristianMurphy/uPortal,jl1955/uPortal5,apetro/uPortal,cousquer/uPortal,Jasig/uPortal,bjagg/uPortal,bjagg/uPortal,mgillian/uPortal,mgillian/uPortal,GIP-RECIA/esco-portail,Jasig/uPortal-start,GIP-RECIA/esup-uportal,cousquer/uPortal,groybal/uPortal,groybal/uPortal,Jasig/uPortal-start,GIP-RECIA/esco-portail,cousquer/uPortal,GIP-RECIA/esup-uportal,GIP-RECIA/esup-uportal,apetro/uPortal,mgillian/uPortal,GIP-RECIA/esup-uportal,jonathanmtran/uPortal