PVF: Add missing crate descriptions (#7587)

polkadot/node/core/pvf/prepare-worker/Cargo.toml

@@ -1,5 +1,6 @@
 [package]
 name = "polkadot-node-core-pvf-prepare-worker"
+description = "Polkadot crate that contains the logic for preparing PVFs. Used by the polkadot-prepare-worker binary."
 version.workspace = true
 authors.workspace = true
 edition.workspace = true

polkadot/node/core/pvf/prepare-worker/src/lib.rs

@@ -14,6 +14,8 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
+//! Contains the logic for preparing PVFs. Used by the polkadot-prepare-worker binary.
+
 mod executor_intf;
 mod memory_stats;