doc: Fix case in titles

Unified case in titles.
Fixed small grammar issues.

Signed-off-by: Francesco Servidio <francesco.servidio@nordicsemi.no>
diff --git a/docs/PORTING.md b/docs/PORTING.md
index 5feb7ac..dd67ffb 100644
--- a/docs/PORTING.md
+++ b/docs/PORTING.md
@@ -1,4 +1,4 @@
-# Porting How-To
+# Porting how-to
 
 This document describes the requirements and necessary steps required to port
 `MCUboot` to a new target `OS`.