Documentation - add Music section and move abc abd fretboard to this section

[brunetton]

I was wondering for a while why ABC music notation is in placed under "UML diagrams" section.

I created a dedicated Music section and put ABC and fretboard onto this section

[jackycute]

Hi @brunetton,

Thanks for the PR and it makes sense.
Could you sign the commit? https://github.com/hackmdio/codimd/blob/develop/CONTRIBUTING.md#sign-your-work

[brunetton]

Hi @brunetton,

Thanks for the PR and it makes sense. Could you sign the commit? https://github.com/hackmdio/codimd/blob/develop/CONTRIBUTING.md#sign-your-work

Done !
And shame on me for not have read the CONTRIBUTING.md file 🤫

[jackycute]

Thanks @brunetton