docs: create pindexer readme and mention pindexer<>pd compat in errors (

#4768)

## Describe your changes

adds some explanation for a common issue with pindexer

## Issue ticket number and link

fixes #4765 

## 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:

indexer-only changes

---------

Signed-off-by: Lúcás Meier <[email protected]>
Co-authored-by: Lúcás Meier <[email protected]>

crates/bin/pindexer/README.md

@@ -0,0 +1,11 @@
+# pindexer
+
+A indexer that ingests ABCI events emitted by pd and transforms them into useful data.
+
+## Usage
+
+1. Follow the setup instructions in cometindex README
+2. `cargo run --bin pindexer -- -s "postgresql://localhost:5432/testnet_raw?sslmode=disable" -d "postgresql://localhost:5432/testnet_compiled?sslmode=disable"`
+
+## pd compatibility
+

crates/bin/pindexer/src/block.rs

@@ -1,3 +1,4 @@
+use crate::PD_COMPAT;
 use anyhow::anyhow;
 use cometindex::{async_trait, sqlx, AppView, ContextualizedEvent, PgTransaction};
 use penumbra_proto::{core::component::sct::v1 as pb, event::ProtoEvent};
@@ -52,7 +53,7 @@ CREATE TABLE IF NOT EXISTS block_details (
         .bind(i64::try_from(pe.height)?)
         .bind(
             DateTime::from_timestamp(timestamp.seconds, u32::try_from(timestamp.nanos)?)
-                .ok_or(anyhow!("failed to convert timestamp"))?,
+                .ok_or(anyhow!(format!("failed to convert timestamp. {PD_COMPAT}")))?,
         )
         .bind(pe.root.unwrap().inner)
         .execute(dbtx.as_mut())

crates/bin/pindexer/src/lib.rs

@@ -7,3 +7,5 @@ pub mod dex;
 pub mod shielded_pool;
 mod sql;
 pub mod stake;
+
+pub(crate) const PD_COMPAT: &'static str = "Check that your pd and pindexer versions match. See pd compatibility section in README for more information.";