📝 Polish onboarding and add feature examples

examples/text_formatter/main.mbt

@@ -0,0 +1,14 @@
+fn main {
+  let formatter = @lib.text_formatter(
+    show_timestamp=false,
+    separator=" | ",
+    field_separator=",",
+    template="[{level}] {target} {message} :: {fields}",
+  )
+  let logger = @lib.Logger::new(
+    @lib.text_console_sink(formatter),
+    min_level=@lib.Level::Info,
+    target="demo.formatter",
+  )
+  logger.info("formatted output", fields=[@lib.field("user", "alice"), @lib.field("request_id", "42")])
+}

examples/text_formatter/moon.pkg

@@ -0,0 +1,7 @@
+import {
+  "Nanaloveyuki/BitLogger/src" @lib,
+}
+
+options(
+  "is-main": true,
+)