Multiple exercises were added to the TypeScript track in this commit.

typescript/nucleotide-count/README.md

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+# Nucleotide Count
+
+Welcome to Nucleotide Count on Exercism's TypeScript Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Each of us inherits from our biological parents a set of chemical instructions known as DNA that influence how our bodies are constructed.
+All known life depends on DNA!
+
+> Note: You do not need to understand anything about nucleotides or DNA to complete this exercise.
+
+DNA is a long chain of other chemicals and the most important are the four nucleotides, adenine, cytosine, guanine and thymine.
+A single DNA chain can contain billions of these four nucleotides and the order in which they occur is important!
+We call the order of these nucleotides in a bit of DNA a "DNA sequence".
+
+We represent a DNA sequence as an ordered collection of these four nucleotides and a common way to do that is with a string of characters such as "ATTACG" for a DNA sequence of 6 nucleotides.
+'A' for adenine, 'C' for cytosine, 'G' for guanine, and 'T' for thymine.
+
+Given a string representing a DNA sequence, count how many of each nucleotide is present.
+If the string contains characters that aren't A, C, G, or T then it is invalid and you should signal an error.
+
+For example:
+
+```text
+"GATTACA" -> 'A': 3, 'C': 1, 'G': 1, 'T': 2
+"INVALID" -> error
+```
+
+## Source
+
+### Created by
+
+- @CRivasGomez
+
+### Contributed to by
+
+- @masters3d
+- @SleeplessByte
+
+### Based on
+
+The Calculating DNA Nucleotides_problem at Rosalind - https://rosalind.info/problems/dna/