Update cheatsheets

tldr/jj-diff

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# jj diff
+
+> Compare file contents between two revisions.
+> More information: <https://jj-vcs.github.io/jj/latest/cli-reference/#jj-diff>.
+
+- Show changes of current revision:
+
+`jj diff`
+
+- Show changes of given revsets (e.g. `B::D`, `A..D`, `B|C|D`, etc.):
+
+`jj diff {{[-r|--revisions]}} {{revsets}}`
+
+- Show changes from given revision to given revision:
+
+`jj diff {{[-f|--from]}} {{from_revset}} {{[-t|--to]}} {{to_revset}}`
+
+- Show diff statistics:
+
+`jj diff --stat`
+
+- Show a Git-format diff:
+
+`jj diff --git`