Update doc and readme

README.md

@@ -131,12 +131,12 @@ Hello Rainbow
 
 This is useful for sharing the same code for logging to console and to a log file.
 
-You can manually change this behavior by either:
+You can manually change this behavior. Rainbow follows these rules in priority:
 
+- Set the `Rainbow.enabled` in your code explicitly.
+- Pass `FORCE_COLOR=1` to enable color even if the output is not a tty. ([`FORCE_COLOR`](https://force-color.org/) has a higher priority than `NO_COLOR`)
+- Pass `NO_COLOR=1` as environment value when executing your app to disable color.
 - Set the `Rainbow.outputTarget` yourself.
-- Pass a `"NO_COLOR"` environment value when executing your app.
-- Or set the `Rainbow.enabled` to `false`.
-
 
 ### Verbose Way
 

Sources/Rainbow.swift

@@ -116,7 +116,8 @@ public enum Rainbow {
     }
 
     /// Enable `Rainbow` to colorize string or not. Default is `true`, unless the `NO_COLOR` environment variable is
-    /// set and `FORCE_COLOR` not set. (`FORCE_COLOR` has higher priority than `NO_COLOR` if set)
+    /// set and `FORCE_COLOR` not set to a valid value ("0" or empty value is treated as "unset". `FORCE_COLOR` has
+    /// higher priority than `NO_COLOR` if set).
     public static var enabled = environmentAvailable
 
     public static func extractEntry(for string: String) -> Entry {