cubicweb-portlets #3195605 Improve documentation regarding column size [validation pending]

The attributes description states "percentage size of the container" which is wrong, as this attribute is interpreted as a weight, the final real column width being

col_width = (html_container_width * col_size / sum(size of the portal columns))
prioritynormal
typeenhancement
done in0.3.1
load0.100
load left0.000
closed by#3b2781b080dd Improve documentation and column size attribute description.
patchImprove documentation and column size attribute description. [applied]