[PATCH v2 3/3] docs: update when `git bisect visualize` uses `gitk`

["Matthias Aßhauer via GitGitGadget" <gitgitgadget@gmail.com>]

From: =?UTF-8?q?Matthias=20A=C3=9Fhauer?= <mha1993@live.de>

This check has involved more environment variables than just `DISPLAY` since
508e84a790 (bisect view: check for MinGW32 and MacOSX in addition to X11,
2008-02-14), so let's update the documentation accordingly.

Signed-off-by: Matthias Aßhauer <mha1993@live.de>
---
 Documentation/git-bisect.txt | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-bisect.txt b/Documentation/git-bisect.txt
index fbb39fbdf5d..bec8d2abb22 100644
--- a/Documentation/git-bisect.txt
+++ b/Documentation/git-bisect.txt
@@ -204,9 +204,14 @@ as an alternative to `visualize`):
 $ git bisect visualize
 ------------
 
-If the `DISPLAY` environment variable is not set, 'git log' is used
-instead.  You can also give command-line options such as `-p` and
-`--stat`.
+Git detects a graphical environment through various environment variables:
+`DISPLAY`, which is set in X Window System environments on Unix systems.
+`SESSIONNAME`, which is set under Cygwin in interactive desktop sessions.
+`MSYSTEM`, which is set under Msys2 and Git for Windows.
+`SECURITYSESSIONID`, which is set on macOS in interactive desktop sessions.
+
+If none of these environment variables is set, 'git log' is used instead.
+You can also give command-line options such as `-p` and `--stat`.
 
 ------------
 $ git bisect visualize --stat
-- 
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