docs(readme): Mention that optional terms ignored

Features list now shows that "optional" terms in the release profile
guide are ignored by default.

Limitations section now states that there is currently no mechanism to
selectively include optional terms.

README.md

@@ -20,6 +20,7 @@ Release Profiles
   name based on the guide and this name is used to find them in subsequent runs.
 - Tags can be added to any updated or created profiles.
 - Ability to convert preferred with negative scores to "Must not contain" terms.
+- Terms mentioned as "optional" in the guide are not synced to Sonarr release profiles.
 
 Quality Definitions
 
@@ -107,6 +108,7 @@ and/or has the following limitations:
 
 - Radarr custom formats are not supported yet (coming soon).
 - Multiple scores on the same line are not supported. Only the first is used.
+- There's no way to explicitly include optional terms to be synced to Sonarr.
 
 ### Roadmap