test-subrepo: document why share magically works even if subrepos are missing
I was confused how it's working while reviewing fb490d798be0, "share: reload
repo after adjusting it in postshare()."
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false