fix for bug 1089: concorde airspeed indicator value at subsonic speeds

updated README.airspeed indicator
added README.systems

Docs/README.airspeed-indicator

@@ -12,14 +12,32 @@ The normal setup is :
     <has-overspeed-indicator>1</has-overspeed-indicator>
   </airspeed-indicator>
 
+Of course the total and static pressure may be sourced from any other 
+pitot and static system when defined:
+
+  <airspeed-indicator>
+    <name>airspeed-indicator</name>
+    <number>1</number>
+    <total-pressure>/systems/pitot[1]/total-pressure-inhg</total-pressure>
+    <static-pressure>/systems/static[1]/pressure-inhg</static-pressure>
+    <has-overspeed-indicator>0</has-overspeed-indicator>
+  </airspeed-indicator>
+
+Note that the Aircraft/Generic/generic-systems.xml only initiates one 
+pitot and one static system, see also README.systems
+
 <total-pressure> is optional --- defaults to "/systems/pitot/total-pressure-inhg"
+For supersonic aircraft with an airspeed indicator NOT compensating for 
+a shockwave in front of the pitot tube (most probably the case), use:
+<total-pressure>/systems/pitot/measured-total-pressure-inhg</total-pressure>
+
 <static-pressure> is optional --- defaults to "/systems/static/pressure-inhg"
 <has-overspeed-indicator> is optional --- defaults to 0 / off
 
 The <has-overspeed-indicator> provides a property for "barber-pole" animation,
  and is set to 0 / false by default ,
 
-If enabled , these properties should be added in the set file ,
+If enabled , these properties should be added in the aircraft -set file,
 with that aircraft's correct figures.
 
     <airspeed-indicator>
@@ -41,3 +59,25 @@ Note : <mach-limit> is the mach limit at <alt-threshold>
 This was designed for indicated airspeed limits, but could probably be extended 
 for mach limits.
 
+
+To initiate additional airspeed indicators, add in your instrumentation 
+file (for airspeed indicator index 1):
+
+  <airspeed-indicator>
+    <name>airspeed-indicator</name>
+    <number>1</number>
+    <total-pressure>/systems/pitot[1]/total-pressure-inhg</total-pressure>
+    <static-pressure>/systems/static[1]/pressure-inhg</static-pressure>
+    <has-overspeed-indicator>0</has-overspeed-indicator>
+  </airspeed-indicator>
+
+Note: this airspeed indicator sources its pressures from the second 
+pitot and static system (with index 1).
+and in the aircraft -set file:
+
+    <airspeed-indicator n="1">
+	  <serviceable type="bool" archive="y">true</serviceable>
+    </airspeed-indicator>
+
+And if "has-overspeed-indicator" = 1, the appropriate limits as explained
+above in the airspeed-indicator brackets.

Docs/README.systems

@@ -0,0 +1,70 @@
+By Default systems are initialized by the Aircraft/generic/generic-system.xml
+This initializes the following:
+- The generic electrical system
+- 1 pitot system, index [0]
+- 1 static system index [0]
+- 2 vacuum systems [0] and [1], depending on engine rpm of engine[0] and
+  engine[1] respectfully
+
+If you want to define more systems, copy the generic-system file to your
+aircraft-name/Systems folder and rename it systems.xml
+
+In your aircraft -set file add the path to the system.xml file:
+<sim>
+    ....
+    <systems>
+        ....
+        <path>Aircraft/aircraft-name/Systems/systems.xml</path>
+        ....
+    </systems> 
+    ....
+</sim>
+
+
+** Adding a second pitot system.
+In your systems.xml, you should already have
+
+  <pitot>
+    <name>pitot</name>
+    <number>0</number>
+  </pitot>
+
+and you need to add for a pitot system with index 1:
+
+  <pitot>
+    <name>pitot</name>
+    <number>1</number>
+  </pitot>
+
+For the any pitot system except for the first (with index 0) 
+add in the aircraft -set file (below for index 1):
+
+<systems>
+      <pitot n="1">
+                <serviceable>1</serviceable>
+      </pitot>
+</systems>
+
+Of course you can add a third or fourth etc.
+
+
+** Adding a second static system
+Absolutely analog with the pitot system. So add in systems.xml:
+
+  <static>
+    <name>static</name>
+    <number>1</number>
+    <tau>1</tau>
+  </static>
+
+and in the aircraft -set file:
+
+<systems>
+      <static n="1">
+                <serviceable>1</serviceable>
+      </static>
+</systems> 
+
+Now you can source your instrumentation relying on static and pitot
+pressure (airspeed, altimeter, vertical speed indicator) from different 
+and independent systems