Issue #2985165 by Liam Morland, ayushmishra206, nbaosullivan, AkashKumar07, valthebald, mathieso, Sutharsan: Improve documentation for BookManagerInterface::saveBookLink()

Issue #2785657 by mathieso, dishabhadra, ifrik, dawehner, YesCT, tim.plunkett: Misleading text in block visibility pages description

Issue #2762173 by megansanicki, artinst4, YesCT, mradcliffe, a_thakur, vermauv, cilefen, mathieso, pwolanin, mlhess: Add "composer install" step to install.txt file for when Drupal is downloaded using git

(cherry picked from commit 4dcb2b1e)