Diary is... well. I will let you have a guess before I tell you.
This Android app lets you write daily entries using Markdown. You can insert images as well.
By default, it will open in the reading mode so your Markdown is rendered as formatted text.
Data is stored in hierarchical folders along with the images, making it easy to back up or sync.
More on development on the Github page:
Diary is available through @fdroidorg:

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