added script to write gtf output

scripts/writegtf.py

+'''
+This function writes keeps the representative transcripts from the original input file (gtf)
+and writes them to an output.
+(The representative transcripts being listed in a csv file)
+'''
+
+def gtf_representative_transcripts(original_gtf, transcripts):
+    transcript = pd.read_csv(transcripts)
+    representative_transcripts = []
+
+    with open (original_gtf, 'r') as file:
+        for id in transcript['id']:
+            for line in file:
+                if id in line:
+                    representative_transcripts.append(line)
+
+
+    with open ('output.gtf', 'w') as outputfile:
+        outputfile.write(representative_transcripts)
+
+