cheat sheet: mark transplanted commits with prime (#2076)

Mark transplanted commits with prime, similar to how manpages
[git-rebase(1)](https://git-scm.com/docs/git-rebase) and
[git-cherry-pick(1)](https://git-scm.com/docs/git-cherry-pick) indicate
them.

## Changes

<!-- List the changes this PR makes. -->

- add a prime symbol (`′` `U+2032`) to letters representing commits
transplanted by
  - `git rebase`
  - `git merge --squash`
  - `git cherry-pick`

## Context

<!-- Explain why you're making these changes. -->
Like in the manpages
[git-rebase(1)](https://git-scm.com/docs/git-rebase) and
[git-cherry-pick(1)](https://git-scm.com/docs/git-cherry-pick), we
should (also in the new cheat sheet) distinguish between a commit and
the commit resulting from transplanting it. They will usually represent
the same change, but they aren't the same commit and might (due to
different ancestors) not have the same file contents in the trees they
refer to (and also some metadata like commit date will differ in
general), thus they aren't the _same_ commit.

The manpages use the straight apostrophe (`'` a.k.a. "single quote") for
this, presumably to stay with ASCII-only for compatibility. I guess the
cheat sheet may dare to use the semantically more precise Unicode
character `PRIME` instead. For source encoding safety, I've used the
corresponding HTML entity.

If I should use the un-escaped Unicode character instead or even just
the ASCII straight apostrophe/single quote, please let me know.

Author: To1ne

content/cheat-sheet/_index.html

@@ -344,8 +344,8 @@ <h3>Combine with rebase:</h3>
             D [label="D", style="dashed", color="#f14e32", pos="2,0!"];
             E [label="E", style="dashed", color="#f14e32", pos="3,0!"];
 
-            D2 [label="D", color="#f14e32", pos="3,1!"];
-            E2 [label="E", color="#f14e32", pos="4,1!"];
+            D2 [label="D&#x2032;", color="#f14e32", pos="3,1!"];
+            E2 [label="E&#x2032;", color="#f14e32", pos="4,1!"];
 
 
             main_label [label="main", shape=plaintext, pos="2,2!", fixedsize=false];
@@ -510,7 +510,7 @@ <h3>Combine with squash merge:</h3>
             C [label="C", pos="2,1!"];
             D [label="D", color="#f14e32", pos="2,0!"];
             E [label="E", color="#f14e32", pos="3,0!"];
-            S [label="D\nE", color="#f14e32", pos="3,1!", width=0.6, height=0.8];
+            S [label="D&#x2032;\nE&#x2032;", color="#f14e32", pos="3,1!", width=0.6, height=0.8];
 
             main_label [label="main", shape=plaintext, pos="5,1!", fixedsize=false];
             main_label -> S [dir=forward];
@@ -655,7 +655,7 @@ <h3>Copy one commit onto the current branch:</h3>
         A [label="A", pos="0,1!"];
         B [label="B", pos="1,1!"];
         C [label="C", pos="2,1!"];
-        D2 [label="D", color="#f14e32", pos="3,1!"];
+        D2 [label="D&#x2032;", color="#f14e32", pos="3,1!"];
 
         D [label="D", color="#f14e32", pos="2,0!"];
         E [label="E", pos="3,0!"];