feat(tldr): add 3rd party fallback completion loader

https://github.com/tldr-pages/tldr-python-client/blob/fa495f2fb9f4a5b35729efa4b83807bc646c8f04/README.md#autocomplete

Note: There is an alternative implementation of tldr [1], which does
not support "--print-completion bash" but provides a separate
completion file [2].  This should not cause a problem because we any
way redirect stderr by "2>/dev/null".

[1] https://github.com/tealdeer-rs/tealdeer
[2] \
https://github.com/tealdeer-rs/tealdeer/blob/769ef4da20dcaa7c00ba638ab11f063b83d99b01/docs/src/installing.md?plain=1#L64

Author: akinomyoga

completions/.gitignore

@@ -426,6 +426,7 @@
 /_timoni
 /_tkn
 /_tkn-pac
+/_tldr
 /_todoist
 /_tofu
 /tracepath6

completions/Makefile.am

@@ -1033,6 +1033,7 @@ CLEANFILES = \
 	_timoni \
 	_tkn \
 	_tkn-pac \
+	_tldr \
 	_todoist \
 	_tofu \
 	tracepath6 \
@@ -1358,7 +1359,7 @@ symlinks: $(DATA)
 	$(ss) koji \
 		arm-koji ppc-koji s390-koji sparc-koji
 	$(ss) _keyring \
-		_glances
+		_glances _tldr
 	$(ss) ldapsearch \
 		ldapadd ldapcompare ldapdelete ldapmodify ldapmodrdn \
 		ldappasswd ldapwhoami