Add info about migrations in INSTALL
Add info about migrations in INSTALL

KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3