docs/quickstart: Tweak Introduction section
docs/quickstart: Tweak Introduction section

Drop the first second level heading as superfluous. Note that the
listing of supported protocols is not actually exhaustive. In the
feature listing, group single thread and non-blocking I/O together.
Fix the name of SystemTap.

Signed-off-by: Jussi Virtanen <2a7e40f91a3be32dfb7e35af6e476a252ebdb4f3@gmail.com>

etoestja/libtrading,jvirtanen/libtrading,Bitcoinsulting/libtrading,NunoEdgarGub1/libtrading,femtotrader/libtrading,fengzhyuan/libtrading,jvirtanen/libtrading,libtrading/libtrading,divaykin/libtrading,fengzhyuan/libtrading,etoestja/libtrading,divaykin/libtrading,penberg/libtrading,femtotrader/libtrading,svdev/libtrading,NunoEdgarGub1/libtrading,penberg/libtrading,mstanichenko/libtrading,svdev/libtrading,Bitcoinsulting/libtrading,mstanichenko/libtrading,libtrading/libtrading