TUTORIAL: minor cleanup

An attempt to make part of the tutorial less jarring, and reformatting
of the surrounding text to keep the lines <80 characters.

Signed-off-by: Joshua Lock <jlock@vmware.com>

docs/TUTORIAL.md

@@ -52,14 +52,14 @@ and verify metadata files.
 To begin, cryptographic keys are generated with the repository tool.  However,
 before metadata files can be validated by clients and target files fetched in a
 secure manner, public keys must be pinned to particular metadata roles and
-metadata signed by role's private keys.  After covering keys, the four required
-top-level metadata are created next.  Examples are given demonstrating the
-expected work flow, where the metadata roles are created in a specific order,
-keys imported and loaded, and metadata signed and written to disk.  Lastly,
-target files are added to the repository, and a custom delegation performed to
-extend the default roles of the repository.  By the end, a fully populated TUF
-repository is generated that can be used by clients to securely download
-updates.
+metadata signed by the role's private keys.  After covering keys, the four
+required top-level metadata are created next.  Examples are given demonstrating
+the expected work flow, where the metadata roles are created in a specific
+order, keys imported and loaded, and metadata signed and written to disk.
+Lastly, target files are added to the repository, and a custom delegation
+performed to extend the default roles of the repository.  By the end, a fully
+populated TUF repository is generated that can be used by clients to securely
+download updates.
 
 ### Keys ###
 The repository tool supports multiple public-key algorithms, such as