fix extant → extent in README

Author: Jorropo

README.md

@@ -47,7 +47,7 @@ Advantages over `bees`:
 - Written in a memory safe language (*hopefully never matter*).
 - Easier to use (just go to the directory and run it).
 - More granular dedup (dedup selected files or directories recursively instead of whole filesystem)
-- File based dedup, does not shard or move extants around on disk,
+- File based dedup, does not shard or move extents around on disk,
   - less fragmentation compared to block based dedup
   - less wear on SSDs.
   - \*shouldn't be undeduped by `btrs fi defrag`.
@@ -71,4 +71,4 @@ This create *reflinks* which are Copy-On-Write that means the files share the on
 
 **Assuming there are no bugs in the kernel**, the worst that can happen is dedup not happening where it should have, it can't corrupt or change the content of your files.
 
-It is also possible to have a bug in Go or thunderdup itself, but that less likely.
+It is also possible to have a bug in Go or thunderdup itself, but that less likely.