Add License file

[bandogora]

Pulled out of #11.

I think it would be beneficial to have a clear project level license; Unless the omission is intentional.

Changes:

• Added License file
  • Copied directly from:

    NibbleAndAHalf/NibbleAndAHalf/base64.h

    Lines 3 to 26 in c3d5edb

    	https://github.com/superwills/NibbleAndAHalf -- Fast base64 encoding and decoding.
    	version 1.0.1, Feb 1, 2022 812a
    	Copyright (C) 2013 William Sherif
    	This software is provided 'as-is', without any express or implied
    	warranty. In no event will the authors be held liable for any damages
    	arising from the use of this software.
    	Permission is granted to anyone to use this software for any purpose,
    	including commercial applications, and to alter it and redistribute it
    	freely, subject to the following restrictions:
    	1. The origin of this software must not be misrepresented; you must not
    	claim that you wrote the original software. If you use this software
    	in a product, an acknowledgment in the product documentation would be
    	appreciated but is not required.
    	2. Altered source versions must be plainly marked as such, and must not be
    	misrepresented as being the original software.
    	3. This notice may not be removed or altered from any source distribution.
    	William Sherif
    	YWxsIHlvdXIgYmFzZSBhcmUgYmVsb25nIHRvIHVz

[bandogora]

@superwills Any thoughts?