.md add link 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: add link in md

[link to google](https://www.google.com)

Example 3: h1 markdown

# H1
## H2
### H3
#### H4
##### H5
###### H6