added troubleshooting for install OSM NBI certificate

### Configuration

### NBI

#### SSL certificate problem

OSM is installed by default using https with a self signed certificated. You will obtain the error '*SSL certificate problem: self signed certificate*' on the client side. To skip this error use the appropriate option to skip certificate validation (e.g. `--insecure` for curl, `--no-check-certificate` for wget, ...). However if for some reason you cannot use this option, you can install this certificate as a valid one in your client system.

To install NBI certificate on the client side (tested for Ubuntu):

Get the certificate file "cert.pem" by one of:

- copy from running docker:

```bash

docker ps | grep nbi

docker cp <docker-id>:/app/NBI/osm_nbi/http/cert.pem .

```

- or from souce code: NBI-folder/osm_nbi/http/cert.pem

- or from etsi git:

```bash

wget -O cert.pem "https://osm.etsi.org/gitweb/?p=osm/NBI.git;a=blob_plain;f=osm_nbi/http/cert.pem;hb=refs/heads/v7.0"

```

Then install this certificate:

```bash

  sudo cp cert.pem /usr/local/share/ca-certificates/osm_nbi_cert.pem.crt

  sudo update-ca-certificates

  # 1 added, 0 removed; done

```

Add to the list of '*/etc/hosts*' a host called "nbi" with the ip address where OSM is running. Can be localhost if client and server are the same machine. Add (or edit) one of these lines:

```text

  127.0.0.1     localhost       nbi

  OSM-ip        nbi

```

Finally for the URL use host 'nbi' <httts://nbi:9999/osm>  (not localhost neither 127.0.0.1). Test it with:

```bash

curl https://nbi:9999/osm/version

```

### VIMs

#### Is the VIM URL reachable and operational?