Add precondition docstings from location comparison

Test: none
Change-Id: Idd3b6d30662b7990effa95b90a22cc3fc67ebc2f
diff --git a/Location.h b/Location.h
index 7407b60..2e99ab8 100644
--- a/Location.h
+++ b/Location.h
@@ -35,6 +35,7 @@
 
     static bool inSameFile(const Position& lhs, const Position& rhs);
 
+    // Precondition: inSameFile()
     bool operator<(const Position& pos) const;
 
    private:
@@ -63,6 +64,7 @@
     static bool inSameFile(const Location& lhs, const Location& rhs);
     static bool intersect(const Location& lhs, const Location& rhs);
 
+    // Precondition: inSameFile() && !intersect()
     bool operator<(const Location& loc) const;
 
    private: