Added documentation

docs/api/scheme/file.md

@@ -4,10 +4,31 @@ The `(scheme file)` library provides procedures for accessing files.
 
 For more information see the [R<sup>7</sup>RS Scheme Specification](../../r7rs.pdf).
 
-- `call-with-input-file`
-- `call-with-output-file`
-- `delete-file`
-- `file-exists?`
-- `with-input-from-file` 
-- `with-output-to-file`
+- [`call-with-input-file` ](#call-with-input-file)
+- [`call-with-output-file`](#call-with-output-file)
+- [`with-input-from-file`](#with-input-from-file)
+- [`with-output-to-file`](#with-output-to-file)
 
+#call-with-input-file
+
+    (call-with-input-file string proc)
+
+Open given filename for input, pass the resulting port to `proc`, and close the port after `proc` returns.
+
+#call-with-output-file
+
+    (call-with-output-file string proc)
+
+Open given filename for output, pass the resulting port to `proc`, and close the port after `proc` returns.
+
+#with-input-from-file
+
+    (with-input-from-file string thunk)
+
+Open given filename for input and change the current input to that port for the duration of `thunk`.
+
+#with-output-to-file
+
+    (with-output-to-file string thunk)
+
+Open given filename for output and change the current output to that port for the duration of `thunk`.