Updated README and CHANGELOG with details about output colors

CHANGELOG.md

@@ -7,6 +7,7 @@ appear at the top.
 
   * Add your entries below here, remember to credit yourself however you want
     to be credited!
+  * Now only color the output if the output IO is associated with a tty or the `SSHKIT_COLOR` environment variable is set. (See [README](README.md#output-colors)) @robd
   * Removed broken support for assigning an `IO` to the `output` config option (See [#243](https://github.com/capistrano/sshkit/issues/243)). @robd
     * Use `SSHKit.config.output = SSHKit::Formatter::SimpleText.new($stdin)` instead
   * Added support for :interaction_handler option on commands. @robd

README.md

@@ -371,6 +371,22 @@ SSHKit.config.output = SSHKit::Formatter::Pretty.new(out)
 SSHKit.config.output = SSHKit::Formatter::SimpleText.new(File.open('log/deploy.log', 'wb'))
 ```
 
+#### Output Colors
+
+By default, SSHKit will color the output using ANSI color escape sequences
+if the output IO you are using is associated with a terminal device (tty).
+This means that you should see colors if you are writing output to the terminal (the default),
+but you shouldn't see ANSI color escape sequences if you are writing to a file.
+
+Colors are supported for the `Pretty` and `Dot` formatters, but for historical reasons
+the `SimpleText` formatter never shows colors.
+
+If you want to force SSHKit to show colors, you can set the `SSHKIT_COLOR` environment variable:
+
+```ruby
+ENV['SSHKIT_COLOR'] = 'TRUE'
+```
+
 #### Custom formatters
 
 Want custom output formatting? Here's what you have to do: