doc + meson.build: update information about foot.ini, small cleanup

- foot.ini.5: mention location of example config file
- foot.1: replace outdated (or incomplete) information about the
  location of the config file with references to foot.ini.5
- foot.1 and foot.ini.5: conform to scdoc specification, thus surround each
  header with (at least) one blank line. additionally consistently use exactly
  one line before/after each header (was sometimes two before)
- foot.1: some parts of the keybindings had their own section, move into
  KEYBOARD SHORTCUTS section
- foot.1: move EXIT STATUS section to the end where it is commonly found
- foot.1: copy information about config file handling from the beginning of
  foot.ini.5 into the CONFIGURATION section of foot.1
- INSTALL.md: foot.ini is no longer included in the documentation
- meson.build: do not bundle foot.ini with documentation anymore, see also
  https://codeberg.org/dnkl/foot/pulls/1015

Closes #1002

meson.build

@@ -266,11 +266,11 @@ if systemd.found()
 endif
 
 scdoc = dependency('scdoc', native: true, required: get_option('docs'))
+install_data('foot.ini', install_dir: join_paths(get_option('sysconfdir'), 'xdg', 'foot'))
 if scdoc.found()
   install_data(
     'LICENSE', 'README.md', 'CHANGELOG.md',
     install_dir: join_paths(get_option('datadir'), 'doc', 'foot'))
-  install_data('foot.ini', install_dir: join_paths(get_option('sysconfdir'), 'xdg', 'foot'))
   subdir('doc')
 endif