Added KSP2 data

Some planet's orbital elements are slightly different from KSP1.

data/systems.yml

@@ -1,6 +1,6 @@
 # File keeping track of the list of solar systems in this data folder
 
-- name: Stock
+- name: Stock (KSP1)
   folderName: stock
 
 - name: JNSQ
@@ -15,6 +15,9 @@
 - name: Real Solar System
   folderName: rss
 
+- name: Stock (KSP2)
+  folderName: stock2
+
 # Template:
 # - name: New Solar System
 #   folderName: new-solar-system