README: update development section

Author: deepfire

README.rst

@@ -416,7 +416,63 @@ Byron vote submission:
 Development
 ****
 
-Development tooling
+Overview
+====
+
+The ``cardano-node`` development is primarily based on the Nix infrastructure (https://nixos.org/ ), which enables packaging, CI, development environments and deployments.
+
+On how to set up Nix for ``cardano-node`` development, please see `Building Cardano Node with nix <https://github.com/input-output-hk/cardano-node/tree/master/doc/getting-started/building-the-node-using-nix.md>`_.
+
+Workbench: a local cluster playground
+====
+
+You can quickly spin up a local cluster, based on any of a wide variety of configurations, and put it under a transaction generation workload -- using the ``workbench`` environment:
+
+1. Optional: choose a workbench profile:
+    - ``default`` stands for a light-state, 6-node cluster, under saturation workload, indefinite runtime
+    - ``ci-test`` is the profile run in the node CI -- very light, just two nodes and short runtime
+    - ``devops`` is an unloaded profile (no transaction generation) with short slots -- ``0.2`` s.
+    - ..and many more -- which can be either:
+        - listed, by ``make ps``
+        - observed at their point of definition: `nix/workbench/profiles/prof1-variants.jq <https://github.com/input-output-hk/cardano-node/tree/master/nix/workbench/profiles/prof1-variants.jq#L333-L526>`_.
+2. Optional: select mode of operation, by optionally providing a suffix:
+    - default -- no suffix -- just enter the workbench shell, allowing you to run ``start-cluster`` at any time.  Binaries will be built locally, by ``cabal``.
+    - ``autostay`` suffix -- enter the workbench shell, start the cluster, and stay in the shell afterwards.  Binaries will be built locally, by ``cabal``.
+    - ``autonix`` suffix -- enter the workbench shell, start the cluster.  All binaries will be provided by the Nix CI.
+    - ..there are other modes, as per `lib.mk <https://github.com/input-output-hk/cardano-node/tree/master/lib.mk>`_.
+3. Enter the workbench shell for the chosen profile & mode:
+    ``make <PROFILE-NAME>`` or ``make <PROFILE-NAME>-<SUFFIX>`` (when there is a suffix).
+4. Optional: start cluster:
+    Depending on the chosen mode, your cluster might already start, or you are expected to start it yourself, using ``start-cluster``.
+
+The workbench services are available only inside the workbench shell.
+
+Using Cabal
+----
+
+By default, all binaries originating in the ``cardano-node`` repository are available to ``cabal build`` and ``cabal run``, unless the workbench was entered using one of the pure ``*nix`` modes.  Note that in all cases, the dependencies for the workbench are supplied though Nix and have been built/tested on CI.
+
+Hoogle
+----
+
+The workbench shell provides ``hoogle``, with a local database for the full set of dependencies:
+
+.. code-block:: console
+
+    [nix-shell:~/cardano-node]$ hoogle search TxId
+    Byron.Spec.Ledger.UTxO newtype TxId
+    Byron.Spec.Ledger.UTxO TxId :: Hash -> TxId
+    Cardano.Chain.UTxO type TxId = Hash Tx
+    Cardano.Ledger.TxIn newtype TxId crypto
+    Cardano.Ledger.TxIn TxId :: SafeHash crypto EraIndependentTxBody -> TxId crypto
+    Cardano.Ledger.Shelley.API.Types newtype TxId crypto
+    Cardano.Ledger.Shelley.API.Types TxId :: SafeHash crypto EraIndependentTxBody -> TxId crypto
+    Cardano.Ledger.Shelley.Tx newtype TxId crypto
+    Cardano.Ledger.Shelley.Tx TxId :: SafeHash crypto EraIndependentTxBody -> TxId crypto
+    Ouroboros.Consensus.HardFork.Combinator data family TxId tx :: Type
+    -- plus more results not shown, pass --count=20 to see more
+
+Supplementary tooling
 ====
 
 GHCID
@@ -428,7 +484,7 @@ Haskell Language Server
 ----
 
 When using Haskell Language Server with Visual Studio Code, you may find that
-`HLINT annotations are ignored<https://github.com/haskell/haskell-language-server/issues/638>`.
+`HLINT annotations are ignored <https://github.com/haskell/haskell-language-server/issues/638>`_.
 
 To work around this, you may run the script ``./scripts/reconfigure-hlint.sh`` to generate a ``.hlint.yaml``
 file with HLINT ignore rules derived from the source code.