selection mode tip

Library/tips.json

 {"tips":[
+"In Selection mode, press C to clear the selection of the current element type.",
 "The BFGS method takes its name from its inventors' initials: Broyden, Fletcher, Goldfarb, and Shanno.",
 "The BFGS and L-BFGS methods tend to converge slowly on near-ill-conditioned problems.",
 "PHT-splines are only <i>C<sup>1</sup></i>-continuous.",