.github: add SUPPORT file
.github: add SUPPORT file

GitHub recently added support for a SUPPORT file:

https://github.com/blog/2400-support-file-support

This SUPPORT file is a very lightly edited copy
of the wiki entry on asking questions:

https://github.com/golang/go/wiki/Questions

Change-Id: Ic1eb74d985ea30862defb99750fb42da84e492de
Reviewed-on: https://go-review.googlesource.com/50930
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

nawawi/go,nawawi/go,Cofyc/go,Cofyc/go,polyverse-security/go,polyverse-security/go,nawawi/go,golang/go,codestation/go,golang/go,akutz/go,akutz/go,codestation/go,codestation/go,cloudflare/go,codestation/go,cloudflare/go,akutz/go,golang/go,polyverse-security/go,codestation/go,codestation/go,vsekhar/elastic-go,vsekhar/elastic-go,polyverse-security/go,Cofyc/go,josharian/go,cloudflare/go,nawawi/go,akutz/go,vsekhar/elastic-go,polyverse-security/go,golang/go,vsekhar/elastic-go,josharian/go,christopher-henderson/Go,polyverse-security/go,josharian/go,cloudflare/go,nawawi/go,codestation/go,CAFxX/go,CAFxX/go,golang/go,cloudflare/go,cloudflare/go,golang/go,CAFxX/go,CAFxX/go,vsekhar/elastic-go,vsekhar/elastic-go,nawawi/go,josharian/go,polyverse-security/go,golang/go,polyverse-security/go,CAFxX/go,josharian/go,akutz/go,akutz/go,cloudflare/go,Cofyc/go,josharian/go,nawawi/go,vsekhar/elastic-go,cloudflare/go,akutz/go,akutz/go,josharian/go,CAFxX/go,golang/go,vsekhar/elastic-go,Cofyc/go,CAFxX/go,nawawi/go,codestation/go,CAFxX/go,josharian/go,Cofyc/go,Cofyc/go,Cofyc/go