Add github action to deploy main branch to openstreetmap.in

[planemad]

From: #36 (comment)

@geohacker

my recommendation would be use the jekyll build gh-pages deploy and wire it up as a Github Action https://github.com/marketplace/actions/jekyll-deploy-gh-pages - I'll do it this weekend and then we can have @satyaakam point the cname to the github DNS.

This would enable seamless updates to the live site directly from github.

[planemad]

Updates to master are automatically reflected on openstreetmap.in now