man: Add even more to the bootchart man page

Essentially transfer the 'README' file in src/bootchart to the man page
for easier reading by users.

Moved the 'History' section to the bottom, before the 'See Also' section.

 man/systemd-bootchart.xml | 100 ++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 83 insertions(+), 17 deletions(-)