intro-text updates
intro-text: fix whitespace
intro-text: apply word-wrap
intro-text: add guidelines for asking for help
intro-text: rewrite the beginning
intro-text: rewrite compiling instructions
intro-text: more rewriting
intro-text small fix
add 'update-lilypond-sources' alias
intro-text: even more rewriting in the end part
intro-text: fix broken link
intro-text: about updating the scripts
fixup! intro-text: add guidelines for asking for help
intro-text: describe merging multiple branches
intro-text: fix typo
Merge 'intro-text' edits into master.