man: Use unveil()

Userland/man.cpp

@@ -37,6 +37,13 @@ int main(int argc, char* argv[])
         return 1;
     }
 
+    if (unveil("/usr/share/man", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    unveil(nullptr, nullptr);
+
     String name;
     String section;