Add new "Atomic File Operations" rule

When file operations after confirming the existence check of a file,
frequent parallel file operations may cause problems that are difficult to reproduce.
Therefore, it is prefer to use atomic file operations.

```ruby
# bad
unless File.exist?(path)
  FileUtils.makedirs(path)
end

if File.exist?(path)
  FileUtils.remove(path)
end

# good
FileUtils.mkdir_p(path)

FileUtils.rm_rf(path)
```

README.adoc

@@ -2185,6 +2185,28 @@ File.open('testfile') do |f|
 end
 ----
 
+Atomic File Operations [[atomic-file-operations]]
+
+When file operations after confirming the existence check of a file, frequent parallel file operations may cause problems that are difficult to reproduce.
+Therefore, it is prefer to use atomic file operations.
+
+[source,ruby]
+----
+# bad
+unless File.exist?(path)
+  FileUtils.makedirs(path)
+end
+
+if File.exist?(path)
+  FileUtils.remove(path)
+end
+
+# good
+FileUtils.mkdir_p(path)
+
+FileUtils.rm_rf(path)
+----
+
 === Standard Exceptions [[standard-exceptions]]
 
 Prefer the use of exceptions from the standard library over introducing new exception classes.