Update INSTALL.txt (added missing --syncdb).
Update INSTALL.txt (added missing --syncdb).

OpenSlides/openslides-votecollector,emanuelschuetze/openslides-votecollector,jwinzer/openslides-votecollector,OpenSlides/openslides-votecollector,OpenSlides/openslides-votecollector,normanjaeckel/openslides-votecollector,normanjaeckel/openslides-votecollector,emanuelschuetze/openslides-votecollector,jwinzer/openslides-votecollector,normanjaeckel/openslides-votecollector,jwinzer/openslides-votecollector,emanuelschuetze/openslides-votecollector