Adding sustain.md

[Jolg42]

I found this not too long ago and I think this is a great idea.

More info about it: https://github.com/sustainers/sustain.md

Here is an example

This markdown file is just as important as a README. It ensures those using this open source software that there are funds coming in as well as a solid back-up plan in case of an debilitating illness, accident, or untimely death.

## Funding
We receive funding from the following:

* https://www.patreon.com/sustainmd-example
* https://opencollective.com/sustainmd-example
* https://flattr.com/creators/@sustainmd-example
* https://en.liberapay.com/sustainmd-example/
* https://example.com/donations
* [Foundation Name](https://example.com/foundation-url)
* [Company Name](https://example.com/company-url)
* [Individual Name](https://example.com/individual-url)

If you or your organization gets value out of this project, please consider donating.

## Bus factor
The following individuals are maintainers and have the skills, know-how, and access to continue this project in case any of them become unavailable due to untimely death, debilitating illness, accident, or any other reason:

* Jane Doe
  * Email: janed@example.com
  * Twitter: @sustainmd-example
  * GitHub: @sustainmd-example
  * Keybase/PGP: https://keybase.io/sustainmd-example


* Joe Boe
  * Email: joeb@example.com
  * Twitter: @sustainmd-example
  * GitHub: @sustainmd-example
  * Keybase/PGP: `B201D628F1302A5E3815B7CEBB28B310B9F90A33`

## Metrics
"You cannot improve what you do not measure." 
Public metrics about this project are available at these locations:

* https://example.com/metrics-dashboard
* https://www.openhub.net/p/example-project
* https://libraries.io/example-tracker/example-project

For the "Bus factor" section, I'll put my info, @fdb can I put yours as well?

For the "Metrics"
https://www.openhub.net/p/opentype_js
https://libraries.io/npm/opentype.js

For the funding part, should we remove it maybe?

[Connum]

For the funding part, should we remove it maybe?

See also #622