Clarify slider and performance status

CHANGELOG.md

@@ -11,6 +11,11 @@ Diff calculation is now significantly faster.
 Difftastic now considers nesting depth when comparing AST nodes, and
 tries to match nodes with similar nesting levels.
 
+Difftastic now prefers marking multiple items on the same line as
+novel, rather than adjacent items on different lines. This helps avoid
+[sliders](https://twitter.com/_wilfredh/status/1411949035871637509),
+where the diff chooses a keyword on the 'wrong' side.
+
 Fixed an issue where complex diffs would not display some unchanged
 lines.
 

README.md

@@ -42,10 +42,9 @@ terminal. It will try to align unchanged nodes (see screenshot above).
 
 Crashes. The code is underdocumented, undertested, and unfinished.
 
-Performance. Difftastic scales poorly on files with a large number of
-changes. This might be solved by A* search.
-
-[Sliders](https://twitter.com/_wilfredh/status/1411949035871637509).
+Performance. Difftastic scales relatively poorly on files with a large
+number of changes, and can use a lot of memory. This might be solved
+by A* search.
 
 Replacing top-level expressions. If you delete a function and write a
 completely different new one, difftastic will show the small number of