xo-reader: + docs scaffold

docs/example.rst

@@ -0,0 +1,45 @@
+.. _examples:
+
+.. toctree::
+   :maxdepth: 2
+
+Examples
+========
+
+See ``xo-reader/examples`` for built examples
+
+.. code-block:: cpp
+   :linenos:
+
+    #include "xo/reader/reader.h"
+
+    int
+    main() {
+        using namespace xo::scm;
+        using namespace std;
+
+        reader rdr;
+        rdr.begin_translation_unit();
+
+        bool eof = false;
+        while (!eof) {
+            auto input = ins.read_some();
+
+            eof = ins.eof();
+
+            for (auto rem = input; !rem.empty();) {
+                // res: (parsed-expr, used)
+                auto [expr, rem2] = rdr.read_expr(rem, eof);
+
+                if (expr) {
+                     cout << expr << endl;
+                }
+
+                rem = rem.suffix_after(rem2);
+            }
+        }
+
+        if (rdr.has_prefix()) {
+            cout << "error: unparsed input after expression" << endl;
+        }
+    }