add link to my script 'get-encryption-key' npm script in BLE.md

[shizuka-na-kazushi]

♻️ Current situation

When using WoSmartLock object, setKey(), user need to obtain encryption key by pySwitchBot script which is written in Python.
Developers who use node-switchbot are familiar with npm/NodeJS, but may have troublesome for using python script.

I just developed NodeJS based script, switchbot-get-encryption-key which is just download by npm.
This script may be more useful for node-switchbot users who want to obtain key ID and encryption key.

💡 Proposed solution

Just adding link to npm page for my script in BLE.md document for developer convenience.

Testing

Click the link in BLE.md file so that there is any link error.

[donavanbecker]

Thanks