docs: add new errors.md

Fixes: #35
7 jobs for exception in 2 minutes and 23 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed flake8 #510201

00:00:52

passed integration #510205

00:01:34

passed pylint #510202

00:01:35

passed self #510204

00:01:42

passed unit #510203

00:01:32

 
  Test Py35
passed self-py35 #510207

00:00:40

passed unit-py35 #510206

00:00:26