Format headings and add bash script build information (#2048)
Format headings and add bash script build information (#2048)

- Explicitly mention that the build can be performed via Powershell as
well as the included bash script.
- Change the note label about ASP.NET Core 1.x into the title which the
note is about for better visibility
- Change all the headings for better readability and separation
MienDev/IdentityServer4,chrisowhite/IdentityServer4,chrisowhite/IdentityServer4,IdentityServer/IdentityServer4,IdentityServer/IdentityServer4,IdentityServer/IdentityServer4,MienDev/IdentityServer4,MienDev/IdentityServer4,chrisowhite/IdentityServer4,MienDev/IdentityServer4,IdentityServer/IdentityServer4