[gspell] docs: readme: summarize list of features

[Sébastien Wilmet <swilmet src gnome org>]

commit 0ac3ed67995bcdb7cc279251eb05a3da84d2d9f9
Author: Sébastien Wilmet <sw swilmet be>
Date:   Wed May 26 03:27:10 2021 +0200

    docs: readme: summarize list of features
    
    This was on the web page.

 README.md | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
---
diff --git a/README.md b/README.md
index 0933c5a..d15d755 100644
--- a/README.md
+++ b/README.md
@@ -3,4 +3,19 @@ gspell - a spell-checking library for GTK applications
 
 gspell provides a flexible API to add spell-checking to a GTK application.
 
+Features
+--------
+
+- Access to basic spell-checking functionality with a GObject-based API.
+- An inline spell-checker for GtkEntry.
+- An inline spell-checker for GtkTextView (enhanced version of
+  [GtkSpell](http://gtkspell.sourceforge.net/)).
+- A spell-checker dialog for GtkTextView.
+- Support of the no-spell-check tag defined by
+  [GtkSourceView](https://wiki.gnome.org/Projects/GtkSourceView).
+- Language choosers (button and dialog).
+
+More information
+----------------
+
 [More information about gspell](docs/more-information.md).