Replace default embed-code with the Go version

[dmytro-kashcheiev]

Currently, the default master version of embed-code is the Ruby-Jekyll version, while only the Go version is in use, making explanations like this one more complex. Additionally, the documentation for embedding is currently located in a separate branch and folder, which can be confusing.

Proposal:

1. Create a branch with the current master version and label it as the Jekyll version of embed-code for backup purposes.
2. Merge the embed-code-go branch into master.
3. Replace the root implementation of embed-code and the corresponding readme.md with the Go version.

IMPORTANT update this guide for code embedders.