inotifywait calls using a variable

Modifies the main script file to allow using the *inotifywait* calls using a variable.

This fixes an issue (on a shared webhost) where calling a startup-script with
cron executes gitwatch when needed. The script threw errors about "inotifywait
not found". *inotify-tools* had been installed by hand to the users home directory,
under `~/bin/`.

By replacing the bare *inotifywait* calls with `/home/[...]/user/bin/inotifywait`
using a script variable fixed the problem, allowing the execution of gitwatch.sh
via a cron-scheduled startup script.

Tested on CentOS, worked fine on shared setup. Tested using

```sh
INOTIFYWAITCMD=inotifywait
```