Updated zfs check (markdown)

zfs-check.md

@@ -2,7 +2,7 @@
 
 ## What does it do?
 
-zfs-check is a tool to generate checksum streams of zfs datasets. (it also can be used on regular block devices and files)
+zfs-check is a tool to generate checksum streams from a zfs datasets. (it also can be used on regular block devices and files)
 
 Its kind of like sha1sum but incremental: It generates a hash per "chunk" of data. This allows you to use it on huge datasets and only do a partial check of the data.
 
@@ -16,6 +16,39 @@ In such cases the checksums are still OK, but they are of the wrong (corrupt) da
 
 So a tool to actually compare the data of 2 datasets was needed, hence zfs-check.
 
+## How to use it?
+
+In its simplest form you can just use it on a directory like this:
+
+```shell
+[root@pve1 ~]# zfs-check /bin --verbose |head -20
+  zfs-check v3.2-alpha2 - (c)2022 E.H.Eefting (edwin@datux.nl)
+  
+  Target               : /bin
+  Block size           : 4096 bytes
+  Block count          : 25600
+  Effective chunk size : 104857600 bytes
+  Skip chunk count     : 0 (checks 100.00% of data)
+  
+smbtree	0	cec00f01df1064a98640e01b50c4030259c655bc
+ls	0	605d772c98dd91c4df9a9200e63c5edf10cff4ce
+cifsdd	0	11348b768b5f14234863c02392dcbe749d34bf91
+dh_bash-completion	0	9d17e0e071892ef43f1ae3fdb5abd40b5bb45252
+swtpm_localca	0	83b427c1ae0d91d46cd49db8ae31e2425e5de55a
+dpkg-mergechangelogs	0	13ec450b69b525bc510bcf15f2409a647928fc43
+true	0	f490cefeec06ba345a5e53ec9814a9763a3330e9
+...
+```
+
+The output of this can then be used as input on another zfs-check. In this example we detected an error:
+
+```shell
+[root@pve1 ~]# zfs-check /bin > checksums
+[root@pve1 ~]# zfs-check /bin --check checksums
+aa-enabled: Chunk 0 failed: c2a2be25e6c3a5d89005028ea37a61771489710a c2a2be25e6c3a5d89005028ea37a61771489710f
+```
+
+It displays the expected sha1sum vs the actual sha1sum)