docs/firmware_flashing.md: fix small grammar issues

Signed-off-by: Michał Żygowski <[email protected]>

Author: miczyg1

docs/firmware_flashing.md

@@ -54,7 +54,7 @@ flashrom -w coreboot.rom -p internal
 
 **IMPORTANT**
 
-To update the firmware and remain the runtime configuration unchanged please
+To update the firmware and keep the runtime configuration unchanged please
 use the following command:
 
 ```
@@ -63,7 +63,7 @@ flashrom -p internal -w apuX_v4.14.0.2.rom --fmap -i COREBOOT
 
 The persistent runtime configuration works only when migrating from versions
 v4.14.0.1 and later. The feature is not yet supported on apu1. Flashrom version
-needs to v1.1 or newer.
+needs to be v1.1 or newer.
 
 A full power cycle is required after flashing. If it is not possible (e.g.
 remote firmware upgrade), when flashing coreboot v4.9.0.4 or newer a full reset