link to other markdown files code example

Example 1: how to create link in readme.md

[a link] (https://github.com/user/repo/blob/branch/other_file.md)

Example 2: markdown link to section in another file

#  Main section

##  [sub-section](./child.md#sub-section)    
##  [sub-section](/child.md#sub-section)
##  [sub-section](child.md#sub-section)