I'm using QGIS 3.4, but this answer should also be possible in 2.18.
Unfortunately it doesn't look like there's a way to directly display the histogram values as part of the histogram. A workaround is to add field values as labels, and manually adjust the placement settings until they line up with the corresponding part of the diagram.
For example, I used multi-line labels with a horizontal histogram. It should be possible to this in any orientation, though.
As you can see the labels aren't perfectly aligned, but I set this up in just a few minutes. You can achieve better alignment with trial and error.
concat() function to concatenate the fields into one long string separated by any one character. Then use that character as the line separator.
Label placement: offset from centroid. Use trial and error to figure out the best values for X,Y Offset (I used X: -3mm, Y: -7mm).
The diagram is right-oriented (layer diagram properties window > options tab)
with default-width bars (5mm) and with scaled size with a bar length of 10.
Diagram placement is "Around centroid".