Tekashi 6ix9ine has been celebrating his release from federal lockup ... but he's gotta be careful and follow strict rules to stay a free man -- or else it's back to the Big House! As everyone knows ... Tekashi was released from MDC Brooklyn after spending 3 months behind bars for running afoul of his conditions of federal probation. The rapper pled guilty to 3 violations -- two for possessing a pair of controlled substances and one for committing an assault. TMZ obtained Tekashi's judgment for