doc: fix documentation for idmapped mounts
[CI:DOCS] fixup for
@@ -27,6 +27,7 @@ The _OPTIONS_ is a comma-separated list and can be: <sup>[[1]](#Footnote1)</sup>
* [**no**]**suid**
* [**r**]**bind**
* [**r**]**shared**|[**r**]**slave**|[**r**]**private**[**r**]**unbindable**
+* **idmap**[=**options**]
The `CONTAINER-DIR` must be an absolute path such as `/src/docs`. The volume
will be mounted into the container at this directory.
@@ -178,3 +179,15 @@ _/foo_, then use **mount --make-shared /** to convert _/_ into a shared mount.
Note: if the user only has access rights via a group, accessing the volume
from inside a rootless <<container|pod>> will fail.
+
+ `Idmapped mount`
+
+If `idmap` is specified, create an idmapped mount to the target user
+namespace in the container. The idmap option supports a custom mapping
+that can be different than the user namespace used by the
+container. The mapping can be specified after the idmap option like:
+`idmap=uids=0-1-10#10-11-10;gids=0-100-10`.
+For each triplet, the first value is the start of the backing file
+system IDs that are mapped to the second value on the host. The
+length of this mapping is given in the third value.
+Multiple ranges are separated with #.
