Added hint that "I.seeEmailAttachment" treats parameter as regular expression

[ngraf]

Motivation/Description of the PR

• Add hint to "I.seeEmailAttachment" that under the hood parameter is treated as RegExp. When you don't know it, it can cause a lot of pain, wondering why your test fails with I.seeEmailAttachment('Attachment(1).pdf') although it looks just fine, but actually I.seeEmailAttachment('Attachment\\(1\\).pdf is required to make the test green, in case the attachment is called "Attachment(1).pdf" with special character in it.

Type of change

• 🔥 Breaking changes
• 🚀 New functionality
• 🐛 Bug fix
• 🧹 Chore
• [ x ] 📋 Documentation changes/updates
• ♨️ Hot fix
• 🔨 Markdown files fix - not related to source code
• 💅 Polish code

Checklist:

• Tests have been added
• Documentation has been added (Run npm run docs)
• Lint checking (Run npm run lint)
• Local tests are passed (Run npm test)