docs: Fix multiple small issues in README.md

Missing information about Stratis support, default value for
`grow_to_fill`, notes about pool type-specific arguments etc.

Resolves: #455

README.md

@@ -46,13 +46,17 @@ keys:
 - `type`
 
   This specifies the type of pool to manage.
-  Valid values for `type`: `lvm`.
+  Valid values for `type`: `lvm`, `stratis`.
 
 - `grow_to_fill`
 
   When set, the pool Physical Volumes will be resized to match their respective device sizes.
   (e.g. after Virtual Machine disk size increase)
 
+  Default: `false`
+
+  __NOTE__: This argument is valid only for LVM pools.
+
 - `shared`
 
   If set to `true`, the role creates or manages a shared volume group. Requires lvmlockd and
@@ -64,6 +68,8 @@ keys:
               destructive operation. The pool itself will be removed as part of the
               process.
 
+  __NOTE__: This argument is valid only for LVM pools.
+
 - `disks`
 
   A list which specifies the set of disks to use as backing storage for the pool.
@@ -107,11 +113,11 @@ keys:
 
 - `encryption_cipher`
 
-  ifies a non-default cipher to be used by LUKS.
+  This string specifies a non-default cipher to be used by LUKS.
 
 - `encryption_key_size`
 
-  s the LUKS key size (in bytes).
+  This integer specifies the LUKS key size (in bytes).
 
 - `encryption_luks_version`