Add minimum town distance patch, with minor modifications

Move implicitly added value of 20 to setting default.
Adjust setting texts.

From: https://www.tt-forums.net/viewtopic.php?p=1095146#p1095146

src/table/settings.ini

@@ -1743,6 +1743,19 @@ from     = 77
 def      = true
 cat      = SC_EXPERT
 
+[SDT_VAR]
+base     = GameSettings
+var      = economy.town_min_distance
+type     = SLE_UINT16
+def      = 20
+min      = 15
+max      = 500
+interval = 5
+str      = STR_CONFIG_SETTING_TOWN_MIN_DISTANCE
+strhelp  = STR_CONFIG_SETTING_TOWN_MIN_DISTANCE_HELPTEXT
+strval   = STR_JUST_INT
+patxname = ""town_min_distance.economy.town_min_distance""
+
 
 [SDT_XREF]
 xref     = ""economy.infrastructure_sharing[0]""