wrote clearer phrasing for config::options::WriteMode::Check

Author: davidbarsky

README.md

@@ -106,8 +106,8 @@ You'll probably want to specify the write mode. Currently, there are modes for
 * `plain` Also writes to stdout, but with no metadata.
 * `diff` Will print a diff between the original files and formatted files to stdout.
          Will also exit with an error code if there are any differences.
-* `check` Similar to `diff`, but is intended to be run in during CI and returns error code 1
-          on failure instead of 4 as `diff` does.  
+* `check` Checks if a diff can be generated. If so, rustfmt outputs a diff and quits with exit code 1.
+          This option is designed to be run in CI-like where a non-zero exit signifies non-standard code formatting. 
 * `checkstyle` Will output the lines that need to be corrected as a checkstyle XML file,
   that can be used by tools like Jenkins.
 

src/config/options.rs

@@ -183,8 +183,8 @@ configuration_option_enum! { WriteMode:
     Checkstyle,
     // Output the changed lines (for internal value only)
     Modified,
-    // Displays how much of the input was processed, but if anything was modified, rustfmt quits
-    // with exit code 0. This option is intended to be run as part of a CI pipeline.
+    // Checks if a diff can be generated. If so, rustfmt outputs a diff and quits with exit code 1.
+    // This option is designed to be run in CI where a non-zero exit signifies non-standard code formatting.
     Check,
 }