Update README troubleshooting and beta scope (#2996)

* Add troubleshooting and remove outdated section from README

* Fix typo

* Add macOS crash reporter troubleshooting

* Remove outdated beta summary

README.md

@@ -12,7 +12,6 @@
 - [About](#about)
 - [Beta Releases](#beta-releases)
 - [Getting Started](#getting-started)
-- [Current Features](#current-features)
 - [Known Issues](#known-issues)
 - [Future Work](#future-work)
 - [Documentation](#documentation)
@@ -76,17 +75,10 @@ These are some of advantages or benefits of Zebra:
 
 Every few weeks, we release a new Zebra beta [release](https://github.com/ZcashFoundation/zebra/releases).
 
-The goals of the beta release series are for Zebra to act as a fully validating Canopy and NU5 node, except for:
+Zebra's network stack is interoperable with `zcashd`,
-
+and Zebra implements all the features required to reach Zcash network consensus.
-- Mempool transactions
-- Block subsidies
-- Transaction fees
-- Some undocumented rules derived from Bitcoin
-- Some consensus rules removed before Canopy activation (Zebra checkpoints on Canopy activation)
-
-Zebra's network stack is interoperable with zcashd.
-Zebra implements all the features required to reach Zcash network consensus.
 
+The goals of the beta release series are for Zebra to act as a fully validating Canopy and NU5 node.
 Currently, Zebra does not validate the following Zcash consensus rules:
 
 #### NU5
@@ -116,10 +108,9 @@ Currently, Zebra does not validate the following Zcash consensus rules:
 - Validation of transaction lock times
 - Validation of sprout note commitment trees
 
-It may be
+#### Other
-unreliable on Testnet, and under less-than-perfect network conditions. See
+- Undocumented rules derived from Bitcoin
-our [current features](#current-features) and [roadmap](#future-work) for
+- Undocumented network protocol requirements
-details.
 
 ## Getting Started
 
@@ -158,11 +149,35 @@ We continuously test that our builds and tests pass on:
 - Ubuntu 18.04 / the latest LTS
 - Debian Buster
 
+Zebra's tests can take over an hour, depending on your machine.
+We're working on making them faster.
+
 `zebrad` might build and run fine on smaller and slower systems - we haven't
 tested its exact limits yet.
 
 For more detailed requirements, refer to the [documentation](https://zebra.zfnd.org/user/requirements.html).
 
+#### Memory Troubleshooting
+
+If Zebra's build runs out of RAM, try setting:
+`export CARGO_BUILD_JOBS=2`
+
+If Zebra's tests timeout or run out of RAM, try running:
+`cargo test -- --test-threads=2`
+
+(cargo uses all the processor cores on your machine by default.)
+
+#### macOS Test Troubleshooting
+
+Some of Zebra's tests deliberately cause errors that make Zebra panic.
+macOS records these panics as crash reports.
+
+If you are seeing "Crash Reporter" dialogs during Zebra tests,
+you can disable them using this Terminal.app command:
+```sh
+defaults write com.apple.CrashReporter DialogType none
+```
+
 ### Network Ports and Data Usage
 
 By default, Zebra uses the following inbound TCP listener ports:
@@ -175,35 +190,13 @@ By default, Zebra uses the following inbound TCP listener ports:
 
 For more detailed information, refer to the [documentation](https://zebra.zfnd.org/user/run.html).
 
-## Current Features
+#### Network Troubleshooting
 
-Network:
+Some of Zebra's tests download Zcash blocks, so they might be unreliable depending on your network connection.
-- Synchronize the chain from peers
+You can set `ZEBRA_SKIP_NETWORK_TESTS=1` to skip the network tests.
-- Maintain a transaction mempool
-- Download gossiped blocks and transactions from peers
-- Answer inbound peer requests for hashes, headers, blocks and transactions
 
-State:
+Zebra may be unreliable on Testnet, and under less-than-perfect network conditions.
-- Persist block, transaction, UTXO, and nullifier indexes
+See our [roadmap](#future-work) for details.
-- Handle chain reorganizations
-
-Proof of Work:
-- Validate equihash, block difficulty threshold, and difficulty adjustment
-- Validate transaction merkle roots
-
-Validating proof of work increases the cost of creating a consensus split
-between `zebrad` and `zcashd`.
-
-This release also implements some other Zcash consensus rules, to check that
-Zebra's [validation architecture](https://zebra.zfnd.org/dev/overview.html#architecture)
-supports future work on a
-full validating node:
-- Block and transaction structure
-- Checkpoint-based verification up to and including Canopy activation
-- Transaction validation (incomplete)
-- Transaction cryptography (incomplete)
-- Transaction scripts (incomplete)
-- Batch verification (incomplete)
 
 ## Known Issues
 
@@ -241,6 +234,11 @@ Performance and Reliability:
 - Batch verification
 - Performance tuning
 
+Currently, the following features are out of scope:
+- Mining support
+- Optional Zcash network protocol messages
+- Consensus rules removed before Canopy activation (Zebra checkpoints on Canopy activation)
+
 ## Documentation
 
 The [Zebra website](https://zebra.zfnd.org/) contains user documentation, such