Mentioning libyaml compile errors in troubleshooting.

README.md

@@ -232,6 +232,17 @@ This should make the client keep the connection alive while validating
 backups.
 
 
+### libyaml compilation errors
+
+borgmatic depends on a Python YAML library (ruamel.yaml) that will optionally
+use a C YAML library (libyaml) if present. But if it's not installed, then
+when installing or upgrading borgmatic, you may see errors about compiling the
+YAML library. If so, not to worry. borgmatic should install and function
+correctly even without the C YAML library. And borgmatic won't be any faster
+with the C library present, so you don't need to go out of your way to install
+it.
+
+
 ## Issues and feedback
 
 Got an issue or an idea for a feature enhancement? Check out the [borgmatic