gitui, tig: improve page descriptions and add "See also"; tig: add example (#12578)

pages/common/gitui.md

@@ -1,6 +1,7 @@
 # gitui
 
-> Terminal UI for Git.
+> A lightweight keyboard-only TUI for Git.
+> See also: `tig`, `git-gui`.
 > More information: <https://github.com/extrawurst/gitui>.
 
 - Specify the color theme (defaults to `theme.ron`):

pages/common/tig.md

@@ -1,7 +1,8 @@
 # tig
 
-> A text-mode interface for Git.
-> More information: <https://github.com/jonas/tig>.
+> A configurable `ncurses`-based TUI for Git.
+> See also: `gitui`, `git-gui`.
+> More information: <https://jonas.github.io/tig/doc/manual.html>.
 
 - Show the sequence of commits starting from the current one in reverse chronological order:
 
@@ -26,3 +27,7 @@
 - Start in stash view, displaying all saved stashes:
 
 `tig stash`
+
+- Display help in TUI:
+
+`h`