Program security - Updated reinitialization-attacks lesson (solana-foundation#406)

* Added updated readme with code, content, grammar and style

* Fixed grammars

* Fixed missing keywords and links

* Update content/courses/program-security/reinitialization-attacks.md

Co-authored-by: Mike MacCana <[email protected]>

* Update content/courses/program-security/reinitialization-attacks.md

Co-authored-by: Mike MacCana <[email protected]>

* Update content/courses/program-security/reinitialization-attacks.md

Co-authored-by: Mike MacCana <[email protected]>

* Updated new repository urls

* Updated content as per starter and solution and guidelines

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Co-authored-by: Mike MacCana <[email protected]>

Author: 0xCipherCoder