README: Link to `docs/src/cli/install.md` to build and install for production (#3698)

[Why]
When I first built the project to run a testnet validator, I looked at
this README by habit with many FOSS projects. `agave-validator` could
not even pass the start-time performance self-check. It took me some
time to understand it was a debug version that I compiled while I was
looking at the other beginner errors like the wrong CPU or the default
governor mode.

[How]
This patch links the build section of the README to the dedicated doc
that explain how to build and install the project for an actual use on
testnet or mainnet.

README.md

@@ -57,6 +57,9 @@ $ cd agave
 $ ./cargo build
 ```
 
+> [!NOTE]
+> Note that this builds a debug version that is **not suitable for running a testnet or mainnet validator**. Please read [`docs/src/cli/install.md`](docs/src/cli/install.md#build-from-source) for instructions to build a release version for test and production uses.
+
 # Testing
 
 **Run the test suite:**