[llvm] [Docs] Update Opt's Option to Specify Pass Pipeline (NFC) (PR #148402)

[Nikita Popov via llvm-commits]

================
@@ -46,12 +46,13 @@ OPTIONS
 
  Write output in LLVM intermediate language (instead of bitcode).
 
-.. option:: -{passname}
+.. option:: --passes=<string>
 
- :program:`opt` provides the ability to run any of LLVM's optimization or
- analysis passes in any order.  The :option:`-help` option lists all the passes
- available.  The order in which the options occur on the command line are the
- order in which they are executed (within pass constraints).
+ A textual (comma separated) description of the pass pipeline
+ e.g.,-passes="foo,bar", to have analysis passes available before a pass, add
----------------
nikic wrote:

```suggestion
 e.g., ``-passes="foo,bar"``, to have analysis passes available before a pass, add
```
Though I'd suggest giving a real example like `-passes=sroa,instcombine`.

https://github.com/llvm/llvm-project/pull/148402