It's totally fine as far as conversational English is concerned. Although the personal pronoun I at the beginning of I edited that in (since the phrase is in the past tense, it means I already did it) is omitted, it's nevertheless understood. It's common practice in spoken English to leave out little words like personal pronouns that go at the beginning of a sentence. Here's the most archetypal example of this practice I can think of:
— Wanna go out tonight?
— Yep. Sounds good. Let's go to a restaurant.
The phrasal verb edit something in means to add something into a piece of text, video or any other type of medium. Edit something out would be an expression that's opposite in meaning. If you edit something out of a piece of text, video etc., you remove it from that piece of text or video.
Some examples:
All swear words and other strong language must be edited out from the clip before uploading it to YouTube because some of our viewers are actually under 16.
— I'd like you to add this to the text.
— Alright, I'll edit it in.