move docs to docs/ folder, rewrite readme and contributing

docs/postfix-syntax.md

@@ -0,0 +1,49 @@
+# Postfix Syntax
+
+Some languages (like Tamil) are grammatically SOV — the condition comes before the keyword, not after. ForeignThon supports this with the `@@` operator.
+
+## How it works
+
+```python
+# Standard prefix (works in every language)
+si x > 0:
+    imprimir(x)
+
+# Postfix with @@
+x > 0 @@si:
+    imprimir(x)
+```
+
+Both produce identical Python: `if x > 0:`. The `@@` means "take whatever is to my left, put the keyword first".
+
+## Rules
+
+- `@@` only rewrites the line it appears on — nothing else changes
+- Indentation rules are identical to normal Python
+- Prefix and postfix can be mixed freely in the same file
+- Works for any keyword in any language pack
+
+## Examples
+
+```python
+# if / else
+x > 0 @@si:
+    imprimir(x)
+sino:
+    pasar
+
+# while
+contador < 10 @@mientras:
+    contador += 1
+
+# inside a function — indentation unchanged
+definir comprobar(x):
+    x > 0 @@si:
+        imprimir("positivo")
+    sino:
+        imprimir("negativo")
+```
+
+## Why @@
+
+`@@` is not valid Python syntax so it never conflicts with existing code. Single `@` is used for decorators and matrix multiplication, so it was ruled out.