[ci skip] Move association class method notes

[loganhasson]

Make explanation of association class methods clearer by moving notes to beginning of each example section.

[arthurnn]

@fxn should we also remove the word Note ?

[loganhasson]

@arthurnn @fxn updated. You're right... Note everywhere seems superfluous.

[dmathieu]

The parenthesis seem to be superfluous too.

[arthurnn]

@loganhasson thanks, can you, also, squash your commits in one?

[loganhasson]

@arthurnn yep, will do. Should I get rid of the parenthesis too?

[arthurnn]

@loganhasson yep please.

[loganhasson]

@arthurnn done and done.

[fxn]

Not convinced about the wording: collection is not being replaced by anything right? It is more of a documentation placeholder... something in that line would be better I believe.

[loganhasson]

@fxn you're right...that wording is strange.

+collection+ is a placeholder for the symbol passed as the first argument, so <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.

slightly better?

[fxn]

👍

[loganhasson]

@fxn @arthurnn fixed

[fxn]

This edit is good, those placeholders are not obvious for a newcomer and this remark is better there upfront. Thanks!

[arthurnn]

thanks ❤️

[loganhasson]

@fxn @arthurnn thanks guys!