Remove discouragement, add developer docs link

[schoen]

Add link to development documentation and remove warning that says SimplicityHL is not yet ready to use.

[stringhandler]

Perhaps we should state the future versions of SimplicityHL may not compile to the same code as previous versions. Or at least "is not guaranteed to match previous versions"

[KyrylR]

Perhaps we should state the future versions of SimplicityHL may not compile to the same code as previous versions. Or at least "is not guaranteed to match previous versions"

Maybe we can do it in the follow up PR as it could need more discussion

[delta1]

Yeah, isn't this used in production already? And if not, it certainly will be soon. Readme can always be updated.

ACK 68813c2

[apoelstra]

Perhaps we should state the future versions of SimplicityHL may not compile to the same code as previous versions. Or at least "is not guaranteed to match previous versions"

I think we're sorta committed to maintaining the current compiler output. Definitely need more discussion to decide the most maintainable way to start improving it.