Mention excluding the `.fragments` directory from version control

[alexander-yevsyukov]

Please add to usage instructions:

1. Adding this directory to .gitignore so that Git does not see these files.
2. Marking this directory as Excluded in IntelliJ IDEA. Right-click on the folder, select the menu item "Mark Directory as/Excluded". Not doing this drives IDEA nuts because the number of files under the directory can be really big, and it takes IDEA indexing them forever after each build.

[Vladyslav-Kuksiuk]

Unnecessary, because we don't have fragments folder.

See: SpineEventEngine/embed-code-go#31