Make it clear that there must be a space between class declaration and curly braces

[panbingkun]

add follow message to section "Spacing and Indentation"
make it clear that there must be a space between class declaration and curly braces

• Put one space between class declaration and curly braces.

  // Correct:
  class Person {
    // some code
  }
  
  // Wrong: omit spaces before curly braces
  class Person{
    // some code
  }