populate-sparsely.sh: explain why the script exits if there is no lock

The reason why the script exits if there is no lock was given in the
commit message when the check was added, but reading the code after some
time I could not remember it, so just put the explanation in a comment
to make the life easier for the reader.

diff --git a/.config/vcsh/hooks-available/populate-sparsely.sh b/.config/vcsh/hooks-available/populate-sparsely.sh
index 387ec21..53d2b3a 100755 (executable)
--- a/.config/vcsh/hooks-available/populate-sparsely.sh
+++ b/.config/vcsh/hooks-available/populate-sparsely.sh
@@ -5,6 +5,9 @@ set -e
 # Only the same instance of vcsh that had the working tree fully populated is
 # allowed to repopulate it sparsely.
 LOCKDIR=/run/lock/vcsh
+
+# If LOCKDIR does not exist it means that the lock is not active so there's no
+# need to do anything.
 [ -d "$LOCKDIR" ] || exit 0
 
 LOCKPID=$(cat "$LOCKDIR/pid")