docs: Build index, tutorial and faq as man pages

This was clearly intended for index, but because it was called "fish"
it was overwritten by the "fish" command man page.

I also added the tutorial and faq. Both of those might not be *ideal*
as man pages (the tutorial makes references to colors that won't show
up), but it's better to provide them than not.

Hat-tip to @wwared

See #5521.

[ci skip]

CHANGELOG.md

@@ -16,6 +16,7 @@
 - `string replace` had an additional round of escaping in the replacement (not the match!), so escaping backslashes would require `string replace -ra '([ab])' '\\\\\\\$1' a`. A new feature flag `string-replace-fewer-backslashes` can be used to disable this, so that it becomes `string replace -ra '([ab])' '\\\\$1' a` (#5556).
 - Some parser errors did not set `$status` to non-zero. This has been corrected (b2a1da602f79878f4b0adc4881216c928a542608).
 - `string` has a new `collect` subcommand that disables newline-splitting on its input. This is meant to be used as the end of a command substitution pipeline to produce a single output argument potentially containing internal newlines, such as `set output (some-cmd | string collect)`. Any trailing newlines are trimmed, just like `"$(cmd)"` substitution in sh. It also supports a `--no-trim-newlines` flag to disable trailing newline trimming, which may be useful when doing something like `set contents (cat filename | string collect -N)` (#159).
+- More of the documentation, including the tutorial, is now available as man pages as well.
 
 ### Syntax changes and new commands
 - Brace expansion now only takes place if the braces include a "," or a variable expansion, so things like `git reset HEAD@{0}` now work (#5869).

sphinx_doc_src/conf.py

@@ -177,7 +177,11 @@ def get_command_description(path, name):
 
 # One entry per manual page. List of tuples
 # (source start file, name, description, authors, manual section).
-man_pages = [(master_doc, "fish", "fish-shell Documentation", [author], 1)]
+man_pages = [
+    (master_doc, "fish-doc", "fish-shell Documentation", [author], 1),
+    ("tutorial", "fish-tutorial", "fish-shell tutorial", [author], 1),
+    ("faq", "fish-faq", "fish-shell faq", [author], 1),
+]
 for path in sorted(glob.glob("cmds/*")):
     docname = strip_ext(path)
     cmd = os.path.basename(docname)