Edit README.md

Edit file for minor grammar and style tweaks, mostly for consistent capitalization and tense across docs.

Author: Amanda Butler

tools/psa/README.md

@@ -1,6 +1,6 @@
-# PSA Tools
+# PSA tools
 
-This document will describe the following scripts:
+This document describes the following scripts:
 
 * \_\_init\_\_.py
 * generate_partition_code.py
@@ -11,18 +11,18 @@ This document will describe the following scripts:
 
 ## \_\_init\_\_.py
 
-This file holds common function dedicated to help SiP with their post-build logic.
-
-* find_secure_image - Scans a Resource object to find the correct binary of the secure image to merge with the non-secure build.
+This file holds common functions dedicated to help SiP with their postbuild logic.
 
+* find_secure_image - Scans a Resource object to find the correct binary of the secure image to merge with the nonsecure build.
 
 ## Code generation scripts
 
-mbed-os holds 2 implementations of PSA:
-* MBED_SPM - Implementation for dual core v7 targets.
+Mbed OS holds two implementations of PSA:
+
+* MBED_SPM - Implementation for dual-core v7 targets.
 * TF-M - Implementation for v8 targets.
 
-each implementation requires a set of auto generated files describing the secure partitions.
+Each implementation requires a set of autogenerated files describing the secure partitions:
 
 * `generate_partition_code.py` - Generate files for both implementations.
 * `generate_mbed_spm_partition_code.py` - Generate files for MBED_SPM.
@@ -31,7 +31,7 @@ each implementation requires a set of auto generated files describing the secure
 
 ## Secure image generation
 
-`release.py` is the script assigned with compiling the secure images.
+`release.py` is the script assigned with compiling the secure images:
 
 ```
 usage: release.py [-h] [-m MCU]
@@ -41,9 +41,10 @@ optional arguments:
   -m MCU, --mcu MCU  build for the given MCU
 ```
 
-when `MCU ` is not specified the script will compile all the images for all the targets
+When `MCU ` is not specified, the script compiles all the images for all the targets.
+
+This script should be run in following scenarios:
 
-This script should be ran in following scenarios:
 * Release.
 * Update to files originating in the secure side.
 * Drivers update.