* part 2 of the initial doc fixes
- spelling fixes
- grammar fixes
- em-dashes should be em-dashes (`—`): double dashes (`--`) are not rendered properly
- reduce overusage of em-dashes, some of those should be separate sentences
- use the correct syntax for notes, tips and warnings
- every sentence is in a separate line (helps with future diffs)
- add missing dots at the end of list items
- fix some lists
* sentences on separate lines in the remaining files
* update docs
* introduce mdbook-admonish for nice looking callouts
* new section on data directory
* recommend source build for advanced users and direct the rest to
binaries
* more strongly highlight that execution client is needed
* write an actual deposit guide
* remove cruft / fix links / etc