Added CMake command to dev docs for linking against librocksdb (#4725)

In the current docs for linking against `libsrockdb`, building
`libsnappy.a` will fail because of an error thrown while building its
third party benchmarks which are enabled by default.

## Describe your changes
This PR adds the CMake CLI option to the docs so that snappy's optional
benchmarks are disabled by default.


## Issue ticket number and link
NA

## Checklist before requesting a review

- [x] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes, for the following reason:

This is a one line change to developer docs for linking against a crate
dependency.

docs/guide/src/dev/build.md

@@ -125,7 +125,7 @@ git submodule update --init
 
 # Build snappy using cmake.
 mkdir build
-cd build && cmake .. && make
+cd build && cmake ../ -DSNAPPY_BUILD_BENCHMARKS=OFF && make
 
 # Add an environment variable pointing to the build/ directory.
 SNAPPY_LIB_DIR=`pwd`