Further refinement of the documentation

Author: screamerbg

README.md

@@ -72,7 +72,7 @@ $ cd mbed-os
 $ mbed update master # updates "mbed-os", not "my-program"
 ```
 
-Also note *mbed CLI* requires that the root of your program is under version control (either Git or Mercurial), which makes it possible to seamlessly switch between revisions the whole program and its libraries/dependencies, synchronize the program with remote repositories; share it with others, and much more. Version control is also the primary/preferred delivery mechanism for mbed OS source code, which allows anyone to contribute back to the OS at any time.
+Also note that *mbed CLI* requires that a program, the root of the code tree, is under version control - either Git or Mercurial. This makes it possible to seamlessly switch between revisions of the whole program and its libraries, control the program history, synchronize the program with remote repositories, share it with others, etc. Version control is also the primary and preferred delivery mechanism for mbed OS source code, which allows everyone to contribute to mbed OS at any time!
 
 *mbed CLI* provides list of all available commnads and global help via `mbed --help`, and also command-specific help via `--help` param to the command, e.g. `mbed update --help`.