glGenerateMipmap() requires OpenGL 3.0

[piernov]

README.md recommends using glGenerateMipmap() which requires OpenGL 3.0 (not available in VirtualBox for example, limited to 2.1, and some older systems). README.md should warn about this requirement and suggest an alternative for OpenGL >= 1.4 && < 3.0:

glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);

or no automatic mipmap generation for OpenGL < 1.4.

https://www.khronos.org/opengl/wiki/Common_Mistakes#Automatic_mipmap_generation