Document license exemptions for contributors.

BINARY_LICENSE

@@ -8,6 +8,9 @@ purposes.
 Further use of the Software requires paying a licensing fee. The actual amount
 and payment methods are stated in the online documentation of the Software.
 
+The copyright owner may exempt certain Users from paying the licensing fee if
+they contributed significantly to the Software development effort.
+
 The automated recurrent installation of the Software is only permitted to paying
 Users.
 

README.md

@@ -182,8 +182,14 @@ Any income left after paying for the infrastructure costs motivates the main
 author to allocate a proportional amount of time on a monthly basis for
 improving the software and supporting existing users.
 
-Note: even though these builds are usually stable enough, they may not have been
-thoroughly tested yet and come with best effort community support.
+Note:
+
+- even though these builds are usually stable enough, they may not have been
+  thoroughly tested yet and come with best effort community support.
+- the authors of significant code contributions and/or their employers are
+  allowed to use these builds free of charge without any time limit. The
+  original author grants these exemptions in written form upon request, and
+  decides on a case by case basis if the contribution is significant enough.
 
 ### Stable builds ###