This plugin will add link on headers for your markdown.
To install, run npm install gatsby-remark-link-on-headers gatsby-transformer-remark.
in gatsby-config, add this under gatsby-transformer-remark:
plugins: [{
//other plugins...
resolve: `gatsby-transformer-remark`,
options: {
plugins: [
{
resolve: `gatsby-remark-link-on-headers`,
options: {
headings: [`h2`, `h3`],
},
},
]
}
}]