Update README.Pico.txt

- fix typos and minor, obvious errors
- reformat small parts
- remove trailing whitespace

README.Pico.txt

@@ -1,18 +1,19 @@
-
 This documentation will explain how to quickly port FLTK to a new
 platform using the Pico driver system. For now, only the sample
-SDL Pico driver on OS X compiles and barely runs.
+SDL Pico driver on macOS compiles and barely runs.
 
 > mkdir build
+> cd build
 > mkdir XcodeSDL
+> cd XcodeSDL
 > cmake -G Xcode -D OPTION_APPLE_SDL=ON ../..
 
-tl;dr - the recent commit should be transparent to all developers 
-on other platforms. On OS X, the CMake setup add the option OPTION_APPLE_SDL=ON 
+tl;dr - the recent commit should be transparent to all developers on
+other platforms. On macOS, the CMake setup adds 'OPTION_APPLE_SDL=ON'
 that will run FLTK on top of SDL, which in turn runs on top of the
 new "Pico" driver set.
 
-The greatest help I can get form the core developers is to continue 
+The greatest help I can get from the core developers is to continue
 to refactor the platform specific functionalities into the drivers.
 
 ---
@@ -40,13 +41,13 @@ have reached goal 1.
 
 "Pico" will implement all driver functionalities "in good faith",
 meaning, in a way that FLTK runs without crashing. Only very very
-basic functions are not implemented. A driver that derives form "Pico" 
+basic functions are not implemented. A driver that derives from "Pico"
 needs only to implement those missing functions, thereby reaching goals
 2 and 3. As far as I can tell, those will be:
 
 - open a single fixed size window
 - setting a pixel in a color inside that window
-- polling and waiting for PUSH and RELEASE events an their position
+- polling and waiting for PUSH and RELEASE events and their positions
 
 By implementing these three simple functions in the SDL driver,
 "test/hello" and quite a bunch of other tests will run (yes, they
@@ -69,6 +70,3 @@ mentioned above, and then go from there.
 
 
 - Matthias
-
-
-