Replace TortoiseBlame with TortoiseGitBlame, TortoiseIDiff with TortoiseGitIDiff, TortoiseMerge with TortoiseGitMerge in documentation

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Use TortoiseGit as example

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>