Doc missing rebase methods (#22556)

* Doc missing rebase methods

* fix wording, explain GIT_REBASE_NO_OPERATION

* clarify the signature

* Imperatives

* enum name and typemax

base/libgit2/rebase.jl

@@ -16,6 +16,14 @@ function Base.count(rb::GitRebase)
     return ccall((:git_rebase_operation_entrycount, :libgit2), Csize_t, (Ptr{Void},), rb.ptr)
 end
 
+"""
+    current(rb::GitRebase) -> Csize_t
+
+Return the index of the current [`RebaseOperation`](@ref). If no operation has
+yet been applied (because the [`GitRebase`](@ref) has been constructed but `next`
+has not yet been called or iteration over `rb` has not yet begun), return
+`GIT_REBASE_NO_OPERATION`, which is equal to `typemax(Csize_t)`.
+"""
 function current(rb::GitRebase)
     return ccall((:git_rebase_operation_current, :libgit2), Csize_t, (Ptr{Void},), rb.ptr)
 end
@@ -52,7 +60,7 @@ end
 """
     LibGit2.commit(rb::GitRebase, sig::GitSignature)
 
-Commits the current patch to the rebase `rb`, using `sig` as the committer. Is silent if
+Commit the current patch to the rebase `rb`, using `sig` as the committer. Is silent if
 the commit has already been applied.
 """
 function commit(rb::GitRebase, sig::GitSignature)
@@ -69,11 +77,27 @@ function commit(rb::GitRebase, sig::GitSignature)
     return oid_ptr[]
 end
 
+"""
+    abort(rb::GitRebase) -> Csize_t
+
+Cancel the in-progress rebase, undoing all changes made so far and returning
+the parent repository of `rb` and its working directory to their state before
+the rebase was initiated. Returns `0` if the abort is successful,
+`LibGit2.Error.ENOTFOUND` if no rebase is in progress (for example, if the
+rebase had completed), and `-1` for other errors.
+"""
 function abort(rb::GitRebase)
     return ccall((:git_rebase_abort, :libgit2), Csize_t,
                       (Ptr{Void},), rb.ptr)
 end
 
+"""
+    finish(rb::GitRebase, sig::GitSignature) -> Csize_t
+
+Complete the rebase described by `rb`. `sig` is a [`GitSignature`](@ref)
+to specify the identity of the user finishing the rebase. Returns `0` if the
+rebase finishes successfully, `-1` if there is an error.
+"""
 function finish(rb::GitRebase, sig::GitSignature)
     return ccall((:git_rebase_finish, :libgit2), Csize_t,
                   (Ptr{Void}, Ptr{SignatureStruct}),