docs/README: Remove references to MICROPY_PORT when building docs.

The docs are now built as one for all ports.

docs/README.md

@@ -21,18 +21,16 @@ preferably in a virtualenv:
 
 In `micropython/docs`, build the docs:
 
-    make MICROPY_PORT=<port_name> html
+    make html
 
-Where `<port_name>` can be `unix`, `pyboard`, `wipy` or `esp8266`.
-
-You'll find the index page at `micropython/docs/build/<port_name>/html/index.html`.
+You'll find the index page at `micropython/docs/build/html/index.html`.
 
 PDF manual generation
 ---------------------
 
 This can be achieved with:
 
-    make MICROPY_PORT=<port_name> latexpdf
+    make latexpdf
 
 but require rather complete install of LaTeX with various extensions. On
 Debian/Ubuntu, try (500MB+ download):