Fixed some grammatical errors in git-rebase.txt documentation.
Fixed some grammatical errors in git-rebase.txt documentation.

Generally, the dependent clause "for example" is suffixed with a comma.
Used present tense where appropriate to be consistent with the other
paragraphs.

Rewrote the paragraph in the second hunk to be more clear.

Signed-off-by: Garry Dolley <3b3734df66674a4ee5e4470c1aa7f153f7a41622@ucla.edu>
Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git