descriptor: improve consistency in use of "digest"

Signed-off-by: Jonathan Boulle <jonathanboulle@gmail.com>

descriptor.md

@@ -63,7 +63,7 @@ The _digest_ property of a Descriptor acts as a content identifier, enabling [co
 It uniquely identifies content by taking a [collision-resistant hash](https://en.wikipedia.org/wiki/Cryptographic_hash_function) of the bytes.
 If the digest can be communicated in a secure manner, one can retrieve the content from an insecure source, recalculate the digest independently, and be certain that the correct content was obtained.
 
-The value of the digest property, the _digest string_, is a serialized hash result, consisting of an _algorithm_ portion (the "algorithm identifier") and a _hex_ portion (the digest).
+The value of the digest property is a string consisting of an _algorithm_ portion (the "algorithm identifier") and a _hex_ portion.
 The algorithm identifier specifies the cryptographic hash function used to calculate the digest; the hex portion is the lowercase hex-encoded result of the hash.
 
 The digest string MUST match the following grammar:
@@ -96,7 +96,7 @@ let verified = ID(C) == D
 ```
 Above, we define the content identifier as `ID(C)`, extracted from the `Descriptor.digest` field.
 Content `C` is a string of bytes.
-Function `H` returns the hash of `C` in bytes and is passed to function `EncodeHex` to obtain the _digest_.
+Function `H` returns the hash of `C` in bytes and is passed to function `EncodeHex` and prefixed with the algorithm to obtain the digest.
 The result `verified` is true if `ID(C)` is equal to `D`, confirming that `C` is the content identified by `D`.
 After verification, the following is true: