[Freeciv-Dev] (PR#16934) improve root_req help

["Per I. Mathisen" <per@xxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=16934 >

Improves the help text for the root_req field of techs.ruleset after some 
confusion in the forums.

   - Per

Index: data/default/techs.ruleset
===================================================================
--- data/default/techs.ruleset  (revision 11947)
+++ data/default/techs.ruleset  (working copy)
@@ -22,9 +22,10 @@
 ;
 ; name          = name as seen by user 
 ; req1, req2   = advances required before researching this one
-; root_req      = advance required before acquiring this one, inherited
-;                 by all techs that require this tech in turn unless
-;                 "None" is given explicitly
+; root_req      = tech required before acquiring this tech, by any
+;     means, inherited by all techs that require this tech in turn unless
+;     "None" is given here explicitly; and you can make a tech available
+;     only through a nation's init_tech by making it root_req itself.
 ; flags         = special flag strings
 ; graphic       = icon for technology
 ; graphic_alt   = alternate icon