Update README.md

Corrects link to the indentation example on the Haskell section.
Add guideline on symbol to_proc

* Using &:method_name is brief but clear
* Using it consistently aids readability
* Preferring simple method calls encourages simple methods
Avoid `link_to` for non-GET requests.

* Using `link_to` with the `method` option introduces an un-necessary
  dependency on JavaScript.
* HTML elements -- in this case a button or a link -- should be chosen for
  their semantics, not their appearance.
* CSS can be used to make links look like buttons and buttons look like
  links.
Add js- prefix to classes as well as ids that use javascript
Remove guideline to prepend js- to ids using javascript
Link to Liftoff

Move Liftoff guideline out of style, which is intended to be mostly
formatting, and into best practices.
Coffeescript preferred styles

* Use `@` instead of `this` for scoping consistency
* Prefer double quotes for consistency
Clarify SRP guideline

The single responsibility principle sounds more appropriate when
referring to a class as a whole rather than an object.
Don't use spaces after unary operators

The current guide suggests spaces around all operators, but we typically don't
add spaces after unary operators, such as `!`.

Adopted from #163.