gofmt: expand page to cover all flags (#23551)

pages/common/gofmt.md

@@ -5,16 +5,28 @@
 
 - Format a file and display the result to the console:
 
-`gofmt {{source.go}}`
+`gofmt {{path/to/source.go}}`
 
 - Format a file, overwriting the original file in-place:
 
-`gofmt -w {{source.go}}`
+`gofmt -w {{path/to/source.go}}`
 
 - Format a file, and then simplify the code, overwriting the original file:
 
-`gofmt -s -w {{source.go}}`
+`gofmt -s -w {{path/to/source.go}}`
 
-- Print all (including spurious) errors:
+- Display diffs instead of rewriting files:
 
-`gofmt -e {{source.go}}`
+`gofmt -d {{path/to/source.go}}`
+
+- List files that would be changed by gofmt:
+
+`gofmt -l {{path/to/directory}}`
+
+- Apply a rewrite rule to the source before reformatting (e.g. replace nil checks with `isNil` calls):
+
+`gofmt -r '{{x == nil -> isNil(x)}}' {{path/to/source.go}}`
+
+- Report all errors, including multiple ones per line:
+
+`gofmt -e {{path/to/source.go}}`