Add an example exploring indentation with comments.

org_mode_samples/comment/indented.org

@@ -0,0 +1,5 @@
+# Comment
+  # indented line
+#        At the top of the file
+foo
+# Another comment

src/parser/comment.rs

@@ -1 +1,10 @@
+use super::Context;
+use crate::parser::error::Res;
+use crate::parser::util::start_of_line;
+use crate::parser::Comment;
 
+#[tracing::instrument(ret, level = "debug")]
+pub fn comment<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Comment<'s>> {
+    start_of_line(context, input)?;
+    todo!()
+}