Add information on how to change indent

[koppor]

What changed with this PR:

More beginner-friendly documentation.

When coming from google-java-format --ASOP or palantir-java-format, it is not that obvious how to use prettier-java. Adding some lines of documentation makes it obvious (and thus this project is more beginner-friendly)

Relative issues or prs:

Fixes #495.

[CLAassistant]

All committers have signed the CLA.

[murdos]

I think it would be better to redirect to the prettier documentation rather than documenting again each configuration parameter.

[koppor]

I think it would be better to redirect to the prettier documentation rather than documenting again each configuration parameter.

My two main reasons:

I aimed for documenting the WTF configuration parameters, not all. Sun Java style is 4 spaces. Nearly all Java code has 4 saves. Default configuration is 2 spaces, which might cause WTF moments.

The prettier configuration is not that obvious for impatient people outside the NodeJS world.

I am open to remove the tab configuration - this is only needed for projects wanting to be more accessible. This might be not worth to make it prominent. Persons caring for exceptional groups are surely able to read and interpet linked documentation.

Some background material,:

Tabs are objectively better than spaces (due to accessibility reasons): https://gomakethings.com/tabs-are-objectively-better-than-spaces/

Another accessibility reason for tabs: when using a braille display, each space takes up one character cell, so indenting with four spaces eats up four cells. Indenting three times with four spaces each eats up 12 characters already. Tabs only take one character cell each, so three indents = three character cells used.

Given many, if not most, braille displays are 40 cells long, and that 70-to 80-cell displays are considered a luxury, and you can see how cutting 12 space characters down to 3 tab characters could be really, really helpful.

• Another article arguing for accessibility: https://alexandersandberg.com/articles/default-to-tabs-instead-of-spaces-for-an-accessible-first-environment/

[koppor]

I got the idea of having the indent configuration in the main README.md from spring-javaformat at https://github.com/spring-io/spring-javaformat#about-the-conventions.