Add comment about long time oscillations

3 jobs for validation-params in 1 minute and 47 seconds (queued for 10 seconds)
Status Name Job ID Coverage
  Build
passed build:package #220780

00:01:26

 
  Test
failed build:documentation #220782

00:00:19

failed test:package #220781

00:00:20

 
Name Stage Failure
failed
test:package Test
-------------------------------------------------------------
TOTAL 1469 1436 615 0 2%

!!!!!!!!!!!!!!!!!!! Interrupted: 9 errors during collection !!!!!!!!!!!!!!!!!!!!
======================== 52 warnings, 9 errors in 1.80s ========================
/usr/local/lib/python3.7/dist-packages/pep8.py:110: FutureWarning: Possible nested set at position 1
EXTRANEOUS_WHITESPACE_REGEX = re.compile(r'[[({] | []}),;:]')
Cleaning up file based variables
ERROR: Job failed: exit code 1
failed
build:documentation Test
  File "<string>", line 1, in <module>
File "/builds/spec-gmt/tkwant-energy-transport/build/lib.linux-x86_64-3.7/tkwant/leads.py", line 28, in <module>
import kwant_spectrum
ModuleNotFoundError: No module named 'kwant_spectrum'

make: *** [Makefile:210: doctest] Error 2
make: Leaving directory '/builds/spec-gmt/tkwant-energy-transport/doc'
Cleaning up file based variables
ERROR: Job failed: exit code 1