The fact that `git lfs clean` needs to compute a SHA-256 signature is
not directly useful to the user. Instead, explain what the user most
needs to know: big file in, pointer file out.
* Such lines conventionally don't end with a full stop, so remove
them.
* Adjust the subsequent `========` lines to have the same length as
the summary lines (the lengths were wrong because of an earlier
renaming of the project).
