README.md: small structure updates

README.md

@@ -19,9 +19,7 @@ Components:
   * `csecsipid`: C STIR/SHAKEN ibrary - wrapper code to build dynamic or static library and .h include files
   * `secsipidx`: `main.go` - CLI tool and HTTP API server for checking or building SIP identity
 
-## secsipidx ##
-
-### Installation ###
+## Installation ##
 
 Install Go language (golang), guidelines at:
 
@@ -87,8 +85,6 @@ openssl ecparam -name prime256v1 -genkey -noout -out ec256-private.pem
 openssl ec -in ec256-private.pem -pubout -out ec256-public.pem
 ```
 
-### Usage ###
-
 #### CLI - Generate Full Identity Header ####
 
 A call from `+493044448888` to `+493055559999` with attestation level `A`, when the public key can be downloaded from `http://asipto.lab/stir/cert.pem`: