Add documentation for translation-work

[zpaceinvader]

Add documentation for how to handle translations, including translating plugins. Include recommendations for plugins/software that might be helpful

[olethomas]

Kept as a reference if #415 is merged:

Package needed:
"wp-cli/i18n-command": "2.4.0"

Command in composer.json:
./vendor/bin/wp i18n make-pot . languages/project-base.pot --exclude=".github,plugins,public/content/plugins,vendor,public/wp,node_modules,tests" --slug=project-base

[WilliamLeeks]

It would be good to have an agreed Dekode approach to translating JavaScript, too. (If it does not already exist.) I think most people are aware of the bug where the MD5 hash does not match the file path — the workaround I have used is manually registering scripts (e.g. for blocks), using wp_set_string_translations(), and manually renaming the JSON files produced by the wp command. I think other people solve it differently, so it would be good to have some docs on the agreed/best method.