README.md: how to substitute a key value from a file

Parameterization of the readme.md file. It is necessary to render the value on the remote github repository using the key specified in the raw readme.md file of the project.

Example:

1. Contents of the .env file:

   root_path=/opt/dirname
   

2. [EXAMPLE] readme.md (raw):

   Current path- `${{root_path}}`
   

3. readme.md (github):

   Current path: /opt/dirname
   

How to do it?