Adds addendum source file (fixes ryanoasis#136)

src/readme-rfn-addendum.md

@@ -0,0 +1,12 @@
+
+What's in a name? The reason for the name change is to comply with the SIL Open Font License (OFL), in partcular the [Reserved Font Name mechanism][SIL-RFN]
+
+Some fonts have parts of their name "reserved" per the [Reserved Font Name mechanism][SIL-RFN]:
+> No Modified Version of the Font Software may use the Reserved Font
+> Name(s) unless explicit written permission is granted by the corresponding
+> Copyright Holder. This restriction only applies to the primary font name as
+> presented to the users.
+
+- The main goals seem to be to: `Avoid collisions`, `Protect authors`, `Minimize support`, and `Encourage derivatives`
+
+See the [Reserved Font Name section][SIL-RFN] for additional information