Grammar and formatting (#257)

* Grammar and formatting

A couple minor tweaks to the README to (hopefully) make it a little bit clearer and easier to follow.

Co-authored-by: per1234 <[email protected]>

Author: obra

README.md

@@ -4,37 +4,50 @@ The repository contains the Arduino APIs and IDE integration files targeting a g
 
 ## Installation
 
-Clone the repository in `$sketchbook/hardware/arduino-git`
+### Clone the repository in `$sketchbook/hardware/arduino-git`
 
 ```bash
 mkdir -p $sketchbook/hardware/arduino-git
 cd $sketchbook/hardware/arduino-git
 git clone [email protected]:arduino/ArduinoCore-mbed mbed
 ```
 
-Then clone https://github.com/arduino/ArduinoCore-API in a directory at your choice.
+### Clone https://github.com/arduino/ArduinoCore-API into a directory of your choice.
 
 ```bash
 git clone [email protected]:arduino/ArduinoCore-API
 ```
 
-Remove the symlink to `api` you can find in  `$sketchbook/hardware/arduino/mbed/cores/arduino` and replace it with a symlink to `ArduinoCore-API/api`
+### Update the `api` symlink
 
-Open Arduino IDE; you should now see three new targets under `MBED boards` label
+Remove the symlink to `api` in `$sketchbook/hardware/arduino/mbed/cores/arduino` and replace it with a symlink to `ArduinoCore-API/api`.
+
+### Test things out
+
+Open the Arduino IDE.
+
+You should now see three new targets under the `MBED boards` label.
+
+*This procedure does not automatically install the required ARM compiler toolchain.*
+
+If the toolchain is missing, you'll see errors like this when you try to build for an mbed-os enabled board.:
 
-You may also need to install ARM build tools if you see an error like the following when you attempt to build for one of the mbed-os enabled boards.
 ```
 fork/exec /bin/arm-none-eabi-g++: no such file or directory
 ```
-The missing ARM build tools can be installed by using the `Boards Manager` option in the Arduino IDE to add the `Arduino mbed-enabled Boards` board package.
+To install ARM build tools, use the `Boards Manager` option in the Arduino IDE to add the `Arduino mbed-enabled Boards` package.
 
 
 ## Adding an mbed target
 
-Adding a target is a mostly automatic procedure that involves running https://github.com/arduino/ArduinoCore-mbed/blob/master/mbed-os-to-arduino after setting `BOARDNAME` and `ARDUINOCORE` env variables.
+Adding a target is a mostly automatic procedure that involves running https://github.com/arduino/ArduinoCore-mbed/blob/master/mbed-os-to-arduino after setting the `BOARDNAME` and `ARDUINOCORE` env variables.
 Actions marked as TODO must be executed manually.
 
-**Minimum Example**: `./mbed-os-to-arduino -r /home/alex/projects/arduino/cores/mbed-os-h747 PORTENTA_H7_M7:PORTENTA_H7_M7`
+**Minimum Example**:
+```
+cd $sketchbook/hardware/arduino-git/mbed
+./mbed-os-to-arduino -r /home/alex/projects/arduino/cores/mbed-os-h747 PORTENTA_H7_M7:PORTENTA_H7_M7
+```
 
 ### How to build a debug version of the Arduino mbed libraries
 * Modify `mbed-os-to-arduino `
@@ -56,4 +69,3 @@ You can use this core as a standard mbed library; all APIs are under `arduino` n
 
 The opposite is working as well; from any sketch you can call mbed APIs by prepending `mbed::` namespace.
 
-