Update README.md

Fixed the problem 84 (Documentation link is broken (404) pycontribs#84)

README.md

@@ -13,12 +13,12 @@ not provided by Python. Read the [documentation](https://tendo.readthedocs.io) f
 - [python tee implementation](https://tendo.readthedocs.io/#module-tendo.colorer) for executing external programs and redirecting their output to both console/file
 - [improved execfile](https://tendo.readthedocs.io/#module-tendo.execfile2)
 
-## Requirements and compatibility
+### Requirements and compatibility
 
 - python 3.8 or newer
 - tox for running tests
 
-## Related projects and packages
+### Related projects and packages
 
 - jaraco - http://pypi.python.org/pypi/jaraco.util
 - pexpect (maybe)