git-rebase.txt: correct antiquated claims about --rebase-merges

When --rebase-merges was first introduced, it only worked with the
`recursive` strategy.  Some time later, it gained support for merges
using the `octopus` strategy.  The limitation of only supporting these
two strategies was documented in 25cff9f ("rebase -i --rebase-merges:
add a section to the man page", 2018-04-25) and lifted in e145d99
("rebase -r: support merge strategies other than `recursive`",
2019-07-31).  However, when the limitation was lifted, the documentation
was not updated.  Update it now.

Acked-by: Johannes Schindelin <[email protected]>
Signed-off-by: Elijah Newren <[email protected]>

Author: newren

Documentation/git-rebase.txt

@@ -1219,12 +1219,16 @@ successful merge so that the user can edit the message.
 If a `merge` command fails for any reason other than merge conflicts (i.e.
 when the merge operation did not even start), it is rescheduled immediately.
 
-At this time, the `merge` command will *always* use the `recursive`
-merge strategy for regular merges, and `octopus` for octopus merges,
-with no way to choose a different one. To work around
-this, an `exec` command can be used to call `git merge` explicitly,
-using the fact that the labels are worktree-local refs (the ref
-`refs/rewritten/onto` would correspond to the label `onto`, for example).
+By default, the `merge` command will use the `recursive` merge
+strategy for regular merges, and `octopus` for octopus merges.  One
+can specify a default strategy for all merges using the `--strategy`
+argument when invoking rebase, or can override specific merges in the
+interactive list of commands by using an `exec` command to call `git
+merge` explicitly with a `--strategy` argument.  Note that when
+calling `git merge` explicitly like this, you can make use of the fact
+that the labels are worktree-local refs (the ref `refs/rewritten/onto`
+would correspond to the label `onto`, for example) in order to refer
+to the branches you want to merge.
 
 Note: the first command (`label onto`) labels the revision onto which
 the commits are rebased; The name `onto` is just a convention, as a nod