readme for std/hash (#6139)

std/hash/README.md

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+# std/hash
+
+## MD5
+
+**Uses:**
+
+```ts
+import { Md5 } from "https://deno.land/std/hash/md5.ts";
+
+const md5 = new Md5();
+const md5Instance = md5.update("中文"); // return instance of `Md5`
+console.log(md5Instance instanceof Md5); // true
+console.log(md5Instance.toString()); // a7bac2239fcdcb3a067903d8077c4a07
+```
+
+Calling `update` method, It will update internal state based on the input
+provided. Once you call `md5Instance.toString()`, it will return the
+`hash string`. You can provide format as `hash` or `base64`. The default format
+is `hex`.
+
+**sample:**
+
+```ts
+console.log(md5Instance.toString("base64")); // MNgWOD+FHGO3Fff/HDCY2w==
+```
+
+## SHA1
+
+**Uses:**
+
+Creating `sha1` hash is simple. You can use `Sha1` class instance and update the
+digest. Calling `hex` method will return the sha1 in hex value. You can also use
+`toString` method.
+
+```ts
+import { Sha1 } from "https://deno.land/std/hash/sha1.ts";
+
+const sha1 = new Sha1().update("中文");
+console.log(sha1.hex()); // 7be2d2d20c106eee0836c9bc2b939890a78e8fb3
+console.log(sha1.toString()); // same as above
+```
+
+## Sha256 and HmacSha256
+
+**Uses:**
+
+Creating `Sha256` hash is simple. You can use `Sha256` class instance and update
+the digest. Calling the `hex` method will return the sha256 in `hex` value. You
+can also use the `toString` method.
+
+**Note:** For `HmacSha256`, you can pass the secret `key` while creating an
+instance of the object.
+
+```ts
+import { Sha256, HmacSha256 } from "https://deno.land/std/hash/sha256.ts";
+
+const sha256 = new Sha256().update("中文");
+console.log(sha256.hex());
+console.log(sha256.toString()); // Same as above
+
+const key = "Hi There";
+const hmac = new HmacSha256(key).update("中文");
+
+console.log(hmac.hex());
+console.log(hmac.toString()); // Same as above
+```