[clang-tools-extra] [clang-tidy][docs] Add documentation for Clang-Tidy Automation (PR #153166)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-armv8-quick` running on `linaro-clang-armv8-quick` while building `clang-tools-extra` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/20436

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests/242/332' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests-Clangd Unit Tests-2597534-242-332.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=332 GTEST_SHARD_INDEX=242 /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests
--

Note: This is test shard 243 of 332.
[==========] Running 4 tests from 4 test suites.
[----------] Global test environment set-up.
[----------] 1 test from CompletionStringTest
[ RUN      ] CompletionStringTest.DocumentationWithAnnotation
[       OK ] CompletionStringTest.DocumentationWithAnnotation (32 ms)
[----------] 1 test from CompletionStringTest (32 ms total)

[----------] 1 test from FuzzyMatch
[ RUN      ] FuzzyMatch.Ranking
[       OK ] FuzzyMatch.Ranking (22 ms)
[----------] 1 test from FuzzyMatch (22 ms total)

[----------] 1 test from CrossFileRenameTests
[ RUN      ] CrossFileRenameTests.WithUpToDateIndex
ASTWorker building file /clangd-test/foo.h version null with command 
[/clangd-test]
clang -xobjective-c++ /clangd-test/foo.h
Driver produced command: cc1 -cc1 -triple armv8a-unknown-linux-gnueabihf -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name foo.h -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -target-cpu generic -target-feature +read-tp-tpidruro -target-feature +vfp2 -target-feature +vfp2sp -target-feature +vfp3 -target-feature +vfp3d16 -target-feature +vfp3d16sp -target-feature +vfp3sp -target-feature +fp16 -target-feature +vfp4 -target-feature +vfp4d16 -target-feature +vfp4d16sp -target-feature +vfp4sp -target-feature +fp-armv8 -target-feature +fp-armv8d16 -target-feature +fp-armv8d16sp -target-feature +fp-armv8sp -target-feature -fullfp16 -target-feature +fp64 -target-feature +d32 -target-feature +sha2 -target-feature +aes -target-feature -fp16fml -target-feature +neon -target-abi aapcs-linux -mfloat-abi hard -debugger-tuning=gdb -fdebug-compilation-dir=/clangd-test -fcoverage-compilation-dir=/clangd-test -resource-dir lib/clang/22 -internal-isystem lib/clang/22/include -internal-isystem /usr/local/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -ferror-limit 19 -fno-signed-char -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fobjc-runtime=gcc -fobjc-encode-cxx-class-template-spec -fobjc-exceptions -fcxx-exceptions -fexceptions -no-round-trip-args -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x objective-c++ /clangd-test/foo.h
Building first preamble for /clangd-test/foo.h version null
not idle after addDocument
UNREACHABLE executed at ../llvm/clang-tools-extra/clangd/unittests/SyncAPI.cpp:22!
#0 0x05165450 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests+0xab5450)
#1 0x05162900 llvm::sys::RunSignalHandlers() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests+0xab2900)
#2 0x05166420 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
#3 0xf0e5d6f0 __default_rt_sa_restorer ./signal/../sysdeps/unix/sysv/linux/arm/sigrestorer.S:80:0
#4 0xf0e4db06 ./csu/../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:47:0
#5 0xf0e8d292 __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
#6 0xf0e5c840 gsignal ./signal/../sysdeps/posix/raise.c:27:6

--
exit: -6
--
shard JSON output does not exist: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/tools/clang/tools/extra/clangd/unittests/./ClangdTests-Clangd Unit Tests-2597534-242-332.json
********************


```

</details>

https://github.com/llvm/llvm-project/pull/153166