Created Error Handling (markdown)

Error-Handling.md

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+Errors are inevitable when working with the API, and they must be correctly handled by the use of `try..except` blocks.
+
+There are many errors that Telegram servers could return, but they all fall in one of these five categories (which are in turn children of the `Error` superclass):
+
+- `(400) BadRequest`
+- `(420) Flood`
+- `(500) InternalServerError`
+- `(303) SeeOther`
+- `(401) Unauthorized`
+
+As stated above, there are really many (too many) errors, and in case Pyrogram does not know anything about a specific error, it raises a special `(520) UnknownError` exception and logs it in the `unknown_errors.txt` file. Users are invited to report these unknown errors; in later versions of Pyrogram some kind of automatic error reporting module might be implemented.
+
+## Examples
+
+``` python
+from pyrogram.api.errors import (
+    BadRequest, Flood, InternalServerError,
+    SeeOther, Unauthorized, UnknownError
+)
+
+try:
+    # Something
+    pass
+except BadRequest:
+    pass
+except Flood:
+    pass
+except InternalServerError:
+    pass
+except SeeOther:
+    pass
+except Unauthorized:
+    pass
+except UnknownError:
+    pass
+```
+
+Exceptions may also contain some informative values which can be useful. e.g. `FloodWait` holds the amount of seconds you have to wait before you can try again. The value is always stored in the `x` field of the returned exception object:
+
+``` python
+from pyrogram.api.errors import FloodWait
+
+try:
+    # something
+    pass
+except FloodWait as e:
+    print(e.x)
+```
+
+**TODO: Better explanation on how to deal with exceptions**