Add info about git diff --check

This is a simple option that helps to check whether you have
a conflict with whitespaces
Add info about git show and reflog

git show if useful option to look at particular commit by it's hash.
It's possible to move on the history like show master@{yesterday}
Add tips about git ranging

There are few possible rangings: double dots, triple dots, multiple points
Git tip about interactive menu to work with staging files
This is very useful and easy: git add -i
Git tip about partial staging
This command is useful if you want to partially commit your changes in the same file
index on master: 5aa25a5 Git tip about partial staging This command is useful if you want to partially commit your changes in the same file
WIP on master: 5aa25a5 Git tip about partial staging This command is useful if you want to partially commit your changes in the same file
Stub for 1837
Git tips about stashes
Add info about stash apply/unapply, list and show
Merge
Git tip about undoings: rebase, ammend, filter-branch
Ignoring temporary ruby project files
Debugging in git: blame, bisect
Those tools help to find when and by whom defect was introduced in code