style: Add comments for bash preexec fix (starship#1952)

* Add comments for bash fix

* Rewrite commend

src/init/starship.bash

@@ -32,6 +32,9 @@ starship_precmd() {
     # Save the status, because commands in this pipeline will change $?
     STATUS=$?
 
+    # Evaluate the number of jobs before running the preseved prompt command, so that tools
+    # like z/autojump, which background certain jobs, do not cause spurious background jobs
+    # to be displayed by starship. Also avoids forking to run `wc`, slightly improving perf
     NUM_JOBS=$(n=0; while read line; do [[ $line ]] && n=$((n+1));done <<< $(jobs -p) ; echo $n)
 
     # Run the bash precmd function, if it's set. If not set, evaluates to no-op