docs: add section about Slack channel invite (#16)

docs: add section about Slack channel invite (#16)

* docs: add section about Slack channel invite

* docs: add Slack step

also update issue template to follow the new format that GitHub uses

* docs: move file to subfolder as required by GitHub

* docs: fix typos and rephrase

Co-Authored-By: timbru31 <ratchet.player@gmx.de>
* docs: fix typo in filename

* docs: type Link -> link

Co-Authored-By: timbru31 <ratchet.player@gmx.de>
* docs: fix commiter -> comitter

Co-Authored-By: timbru31 <ratchet.player@gmx.de>
* docs: `` instead of ''

Co-Authored-By: timbru31 <ratchet.player@gmx.de>
* docs: `` instead of ''

Co-Authored-By: timbru31 <ratchet.player@gmx.de>
* docs: `` instead of ''

Co-Authored-By: timbru31 <ratchet.player@gmx.de>
* docs: Link -> link