naming: Add style guidance for Merlinite and Granite

This came up in review on instructlab#70, so document the preferred
capitalization.

Signed-off-by: Russell Bryant <rbryant@redhat.com>

Author: russellb

Diff for: docs/naming-conventions.md

@@ -7,3 +7,8 @@
   (like Slack)
 * `InstructLab` - CamelCase when referring to the name of the overall project.
 * Never `Instruct Lab` with a space.
+
+## Models
+
+* `Merlinite` and `Granite` are capitalized unless referring to a filename
+  like `merlinite-7b-lab-Q4_K_M.gguf`.