Improve readability of salting description

Add a comma in the final sentence of the description of salting, to
improve the readability of what's being said.

doc/security/password_storage.md

@@ -10,4 +10,4 @@ GitLab uses the [Devise](https://github.com/plataformatec/devise) authentication
 
 - **Hashing**: the [bcrypt](https://en.wikipedia.org/wiki/Bcrypt) hashing function is used to generate the hash of the provided password. This is a strong, industry-standard cryptographic hashing function.
 - **Stretching**: Password hashes are [stretched](https://en.wikipedia.org/wiki/Key_stretching) to harden against brute-force attacks. GitLab uses a stretching factor of 10 by default.
-- **Salting**: A [cryptographic salt](https://en.wikipedia.org/wiki/Salt_(cryptography)) is added to each password to harden against pre-computed hash and dictionary attacks. Each salt is randomly generated for each password, so that no two passwords share a salt to further increase security.
+- **Salting**: A [cryptographic salt](https://en.wikipedia.org/wiki/Salt_(cryptography)) is added to each password to harden against pre-computed hash and dictionary attacks. Each salt is randomly generated for each password, so that no two passwords share a salt, to further increase security.