Update README to include Andrew Fawcett's lecture

[evelyn-fyi]

Describe the bug
duplicate link in README - Advanced Apex Design Patterns by Andy Fawcett should link to https://www.youtube.com/watch?v=BLXp0ZP0cF0

[john-storey-devops]

PR #102

[john-storey-devops]

@evelyn-fyi, thanks for pointing it out! PR up for it.