Instead of 'yes' show the defense cap value in help.

Suggested by Soliton. Also add a line of explanation in the help
that although a value is shown, if there is a cap it is always
the same as the defensive rating of the unit on that terrain and
cannot be larger.

data/core/help.cfg

@@ -496,7 +496,9 @@ Terrains come in two types: <italic>text='basic'</italic> terrain types and <ita
 
 You can see what basic types are associated to a mixed type by mousing over its hex and checking the terrain type icons displayed in the upper right, under the default theme." + _"
 
-Some units have <italic>text='defense caps'</italic> for a particular basic terrain type. In that case, the 'best defense' behavior is overridden -- they can never recieve a higher defense rating than the lowest defense cap value for any mixed terrain type which includes that basic type. For example, the loyalist cavalryman has a defense rating of 30% on forests, and a defense cap for forests. Thus, on forested hills, he has a defense rating of 30% rather than 40%, because the mixed rating cannot exceed the cap.
+Some units have <italic>text='defense caps'</italic> for a particular basic terrain type. In that case, the 'best defense' behavior is overridden -- they can never recieve a higher defense rating than the lowest defense cap value for any mixed terrain type which includes that basic type. For example, the loyalist cavalryman has a defense rating of 30% on forests, and a defense cap for forests. Thus, on forested hills, he has a defense rating of 30% rather than 40%, because the mixed rating cannot exceed the cap." + _"
+
+If a unit has a defense cap for some terrain, it is always the same as its defense rating on that terrain (it cannot be larger)." + _"
 
 <header>text='Basic Terrain Types'</header>
 

src/help.cpp

@@ -1816,14 +1816,14 @@ class unit_topic_generator: public topic_generator
 						str.str(clear_stringstream);
 						const bool has_cap = movement_type.get_defense().capped(terrain);
 						if (has_cap) {
-							str << "<format>color=yellow text='yes'</format>";
+							str << "<format>color=yellow text='" << defense << "%'</format>";
 						} else {
 							str << "<format>color=white text='" << utils::unicode_figure_dash << "'</format>";
 						}
 						markup = str.str();
 						str.str(clear_stringstream);
 						if (has_cap) {
-							str << "yes";
+							str << defense << '%';
 						} else {
 							str << utils::unicode_figure_dash;
 						}