set paragraph to massive description

Signed-off-by: xiekeyang <[email protected]>

Author: xiekeyang

image-layout.md

@@ -44,11 +44,14 @@ afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51 ./blobs/sha256/
 ```
 
 Object names in the `refs` subdirectories MUST NOT include characters outside of the set of "A" to "Z", "a" to "z", "0" to "9", the hyphen `-`, the dot `.`, and the underscore `_`.
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 Object names in the `blobs` subdirectories are composed of a directory for each hash algorithm, the children of which will contain the actual content.
 A blob, referenced with digest `<alg>:<hex>` (per [descriptor](descriptor.md#digests-and-verification)), MUST have its content stored in a file under `blobs/<alg>/<hex>`.
 The character set of the entry name for `<hex>` and `<alg>` MUST match the respective grammar elements described in [descriptor](descriptor.md#digests-and-verification).
 For example `sha256:5b` will map to the layout `blobs/sha256/5b`.
+
 The blobs directory MAY contain blobs which are not referenced by any of the refs.
+
 The blobs directory MAY be missing referenced blobs, in which case the missing blobs SHOULD be fulfilled by an external blob store.
 
 No semantic restriction is given for object names in the `refs` subdirectory.