docs: clarify bootable and revertable parameter precedence and conflict handling

Update documentation for both snapshot_lvm_bootable and snapshot_lvm_revertable
to explicitly describe:
- The two configuration locations (global vs. set-level)
- Precedence rules (global takes precedence when set)
- Conflict behavior (ERROR_BOOTABLE_CONFLICT or ERROR_REVERTABLE_CONFLICT)
- That no snapshot is created when conflicting values are detected

This addresses potential confusion about parameter precedence and makes it
clear that conflicting values will cause the role to fail rather than
silently choosing one value over the other.

Signed-off-by: Todd Gill <tgill@redhat.com>

Author: trgill

README.md

@@ -332,13 +332,41 @@ support snapshot manager (snapm).  When set to true, and passed to the
 'snapshot' command, the snapshot created will have a corresponding boot
 entry.  The boot entry will be removed when the snapset is removed.
 
+This parameter can be set in two locations:
+
+- **Global level**: `snapshot_lvm_bootable: true` applies to all snapshots
+- **Set level**: `bootable: true` in the `snapshot_lvm_set` definition
+
+**Precedence and conflict handling:**
+
+- If the global parameter is set, it takes precedence
+- If both global and set-level parameters are set to **different** values
+  (e.g., global is `true` and set-level is `false`), the role will fail with
+  `ERROR_BOOTABLE_CONFLICT` and no snapshot will be created
+- If both are set to the **same** value, the operation proceeds normally
+- If only one is set, that value is used
+
 ### snapshot_lvm_revertable
 
 Boolean - default is false.  Only supported on operating systems that
 support snapshot manager (snapm) version 0.5.0 or later.  When set to true,
 and passed to the 'snapshot' command, the snapshot created will have a
 corresponding revert boot entry.
 
+This parameter can be set in two locations:
+
+- **Global level**: `snapshot_lvm_revertable: true` applies to all snapshots
+- **Set level**: `revertable: true` in the `snapshot_lvm_set` definition
+
+**Precedence and conflict handling:**
+
+- If the global parameter is set, it takes precedence
+- If both global and set-level parameters are set to **different** values
+  (e.g., global is `true` and set-level is `false`), the role will fail with
+  `ERROR_REVERTABLE_CONFLICT` and no snapshot will be created
+- If both are set to the **same** value, the operation proceeds normally
+- If only one is set, that value is used
+
 To perform a disaster recovery revert:
 
 1. Run `snapshot_lvm_action: revert` to initiate the revert operation