Cleaning up README language about new `rbenv` feature.

README.md

@@ -498,11 +498,11 @@ This segment shows the version of Ruby being used when using `rbenv` to change y
 It figures out the version being used by taking the output of the `rbenv version-name` command.
 
 * If `rbenv` is not in $PATH, nothing will be shown.
-* If the current Ruby version is the same as the global Ruby version, nothing will be shown.
+* By default, if the current local Ruby version is the same as the global Ruby version, nothing will be shown. See the configuration variable, below, to modify this behavior.
 
 Variable | Default Value | Description |
 |----------|---------------|-------------|
-|`POWERLEVEL9K_RBENV_ALWAYS`|'false'|Always show rbenv version, even if global|
+|`POWERLEVEL9K_RBENV_ALWAYS`|'false'|Always show the `rbenv` segment, even if the local version matches the global.|
 
 ##### rspec_stats