No, the contents letter is the optional letter written by your husband.
Your letter should include details of how you meet each visa requirement (financial, accommodation and relationship), plus a list of the documents YOU are providing towards the application to support what you've said in the letter - so your financial and accommodation documents and your passport copy (not a full list of every document being mailed).
The information about your relationship should be short and to the point... They just need to know where and when you met, what date you married, how you keep in contact while apart and why you are going to live in the UK.
Something like:
'We started communicating online on Facebook on X date and flew to ***** to meet each other in person on Y date. We visited each other Z times before getting engaged on A date. We flew to B country and married on C date, then after our honeymoon, I returned to work in the UK while he prepared his spousal visa application from the US. We have chosen to settle in the UK because of D reasons.'
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