add basic documentation

README.md

@@ -1,3 +1,124 @@
 # ggemtext
 
 Glib-oriented [Gemtext](https://geminiprotocol.net/docs/gemtext.gmi) API
+
+## Install
+
+``` bash
+cargo add ggemtext
+```
+
+## Usage
+
+### Line
+
+Line parser, useful for [TextTag](https://docs.gtk.org/gtk4/class.TextTag.html) operations in [TextBuffer](https://docs.gtk.org/gtk4/class.TextBuffer.html) context.
+
+**Connect dependencies**
+
+``` rust
+use ggemtext::line::{
+    code::Code,
+    header::{Header, Level},
+    link::Link,
+    list::List,
+    quote::Quote,
+};
+```
+
+**Prepare document**
+
+Iterate Gemtext lines to continue with [Line](#Line) API:
+
+``` rust
+for line in gemtext.lines() {
+    // ..
+}
+```
+
+#### Code
+
+##### Inline
+
+``` rust
+match Code::inline_from("```inline```") {
+    Some(inline) => assert_eq!(inline.value, "inline"),
+    None => assert!(false),
+};
+```
+
+##### Multiline
+
+``` rust
+match Code::multiline_begin_from("```alt") {
+    Some(mut multiline) => {
+        Code::multiline_continue_from(&mut multiline, "line 1");
+        Code::multiline_continue_from(&mut multiline, "line 2");
+        Code::multiline_continue_from(&mut multiline, "```"); // complete
+
+        assert!(multiline.completed);
+        assert_eq!(multiline.alt, Some("alt".into()));
+        assert_eq!(multiline.buffer.len(), 3);
+    }
+    None => assert!(false),
+};
+```
+
+#### Header
+
+``` rust
+match Header::from("# H1") {
+    Some(h1) => {
+        assert_eq!(h1.level as i8, Level::H1 as i8);
+        assert_eq!(h1.value, "H1");
+    }
+    None => assert!(false),
+}; // H1, H2, H3
+```
+
+#### Link
+
+``` rust
+match Link::from(
+    "=> gemini://geminiprotocol.net 1965-01-19 Gemini",
+    None, // absolute path given, base not wanted
+    Some(&gtk::glib::TimeZone::local()),
+) {
+    Some(link) => {
+        // Alt
+        assert_eq!(link.alt, Some("Gemini".into()));
+
+        // Date
+        match link.timestamp {
+            Some(timestamp) => {
+                assert_eq!(timestamp.year(), 1965);
+                assert_eq!(timestamp.month(), 01);
+                assert_eq!(timestamp.day_of_month(), 19);
+            }
+            None => assert!(false),
+        }
+
+        // URI
+        assert_eq!(link.uri.to_string(), "gemini://geminiprotocol.net");
+    }
+    None => assert!(false),
+};
+```
+
+#### List
+
+``` rust
+match List::from("* Item") {
+    Some(list) => assert_eq!(list.value, "Item"),
+    None => assert!(false),
+};
+```
+
+#### Quote
+
+``` rust
+match Quote::from("> Quote") {
+    Some(quote) => assert_eq!(quote.value, "Quote"),
+    None => assert!(false),
+};
+```