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

[Baranov Victor via cfe-commits]

================
@@ -331,6 +331,106 @@ An overview of all the command-line options:
         some-check.SomeOption: 'some value'
       ...
 
+Clang-Tidy Automation
+=====================
+
+:program:`clang-tidy` can analyze multiple source files by specifying them on the
+command line or by using a compilation database. For larger projects, automation
----------------
vbvictor wrote:

```suggestion
command line. For larger projects, automation
```
Just by specifying a database doesn't mean that `clang-tidy` will run over all of those files, so I'd remove this part.

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