Create README.md

Added how the program works and a disclaimer at the end.

README.md

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+# DNA_transcription_translation
+A simple, fast program which transcribes a DNA strand into messenger RNA (mRNA), which it then translates into amino acids.
+## What does it do? ##
+It takes in a DNA strand as input and converts this strand to a complementary messenger RNA strand using these mappings:  
+  
+A → U  
+T → A  
+C → G  
+G → C  
+  
+For example, `GTACTAGAGCATTT` would be converted to `CAUGAUCUCGUAAA`  
+After this, it looks for a start codon (AUG) and a stop codon (UAA, UAG, UGA) and it removes anything out of the range from start to stop.  
+For example, `CAUGAUCUCGUAAA` would be converted to `AUGAUCUCGUAA`  
+Then, it turns the result of the previous step into a list broken into 3-character items.  
+For example, `AUGAUCUCGUAA` would be converted to `['AUG', 'AUC', 'UCG', 'UAA']`  
+Finally, it compares each item in the list to the amino_acids.py file, which is basically a predefined [codon chart.](https://www.google.com/search?q=codon+chart&rlz=1C1CHBF_enUS912US912&tbm=isch&source=iu&ictx=1&fir=SVhfz4tRL5GzVM%252Cx4w9lB13r4FJ7M%252C_&vet=1&usg=AI4_-kSuwWL4sbNFjTZd3fkSLRoPujadRw&sa=X&ved=2ahUKEwi7verdq-7sAhVQSK0KHUXZAp8Q9QF6BAgBEFg&biw=1366&bih=625&safe=active&ssui=on#imgrc=SVhfz4tRL5GzVM)  
+This returns a list of the amino acids for the codons: `['AUG', 'AUC', 'UCG', 'UAA']` would return `['Methionine', 'Isoleucine', 'Serine', 'STOP']`  
+
+**WARNING: I HAVEN'T DONE A LOT OF TESTING, SO USE THIS TOOL AT YOUR OWN RISK.**