Show manual test instructions in verbose mode

Include instructions for the manual test execution in verbose mode
of the `tmt test show` command.

tmt/base.py

@@ -1339,6 +1339,24 @@ def enabled_on_guest(self, guest: tmt.steps.provision.Guest) -> bool:
 
         return any(destination in (guest.name, guest.role) for destination in self.where)
 
+    def show_manual(self) -> None:
+        """ Show manual test instructions """
+
+        if self.tree is None or self.tree.root is None:
+            return
+
+        if self.test is None or self.test._script is None:
+            return
+
+        instructions_path = self.tree.root / self.test._script
+
+        try:
+            instructions = instructions_path.read_text()
+            echo(tmt.utils.format('instructions', instructions))
+
+        except FileNotFoundError:
+            self.warn(f"Manual test instructions file '{instructions_path}' not found.")
+
     def show(self) -> None:
         """ Show test details """
         self.ls()
@@ -1371,6 +1389,11 @@ def show(self) -> None:
                 continue
             if value not in [None, [], {}]:
                 echo(tmt.utils.format(key, value))
+
+            # Show test instructions for manual tests in verbose mode
+            if key == "manual" and self.manual and self.verbosity_level:
+                self.show_manual()
+
         if self.verbosity_level:
             self._show_additional_keys()
         if self.verbosity_level >= 2: