README: Update, more details about package sources.

README.md

@@ -3,11 +3,17 @@ micropython-lib
 micropython-lib is a project to develop a non-monolothic standard library
 for MicroPython (https://github.com/micropython/micropython). Each module
 or package is available as a separate distribution package from PyPI. Each
-module is either written from scratch or ported from CPython.
+module comes from one of the following sources (and thus each module has
+its own licensing terms):
+
+* written from scratch specifically for MicroPython
+* ported from CPython
+* ported from some other Python implementation, e.g. PyPy
+* some modules actually aren't implemented yet and are dummy
 
 Note that the main target of micropython-lib is a "Unix" port of MicroPython.
-Actual system requirements vary per module. Though if a module is not related
+Actual system requirements vary per module. For example, if a module is not
-to I/O, the module should work without problems on bare-metal ports too (e.g.
+related to I/O, it may work without problems on bare-metal ports too (e.g.
 pyboard).
 
 
@@ -17,11 +23,12 @@ micropython-lib packages are published on PyPI (Python Package Index),
 the standard Python community package repository: http://pypi.python.org/ .
 On PyPI, you can search for MicroPython related packages and read
 additional package information. By convention, all micropython-lib package
-names are prefixed with "micropython-".
+names are prefixed with "micropython-" (the reverse is not true - some
+package starting with "micropython-" aren't part of micropython-lib and
+were released by 3rd parties).
+
 Browse available packages
 [via this URL](https://pypi.python.org/pypi?%3Aaction=search&term=micropython).
-(Note: search results may include both micropython-lib and 3rd-party
-packages).
 
 To install packages from PyPI for usage on your local system, use the
 `upip` tool, which is MicroPython's native package manager, similar to