feat(makechrootpkg): Add "-i" to install packages from repository.

Technically it should be within the PKGBUILD file, but just having this parameter makes scripting and automating makechrootpkg much easier in the cases it doesn't. Otherwise one would have to handle patching the PKGBUILD which may fail once the file gets updated, where as just manually installing a package is almost always successful and therefore much better for scripted/automated usage. Also just having this option simplifies debugging side effects and dependency errors using clean builds that have specific additional packages installed.

E.g. makechrootpkg -c -u -T -U builduser -n -C -r /aur_chroot -i suspectedpackage