Improve documentation

[amotl]

About

Significantly improve the README, guiding the dear reader into the topics of Singer, the Singer Spec, Meltano, and PipelineWise.

Add two usage examples:

1. Show Meltano YAML configuration snippet right away.

   - name: target-cratedb
     namespace: cratedb
     variant: cratedb
     pip_url: meltano-target-cratedb
     config:
       sqlalchemy_url: crate://crate@localhost/
       add_record_metadata: true

2. Instructions how to load a data file in Singer format (JSONL) in standalone mode.

   # Acquire, configure, invoke -- at a glance.
   wget https://github.com/MeltanoLabs/target-postgres/raw/v0.0.9/target_postgres/tests/data_files/tap_countries.singer
   echo '{"sqlalchemy_url": "crate://crate@localhost/"}' > settings.json
   cat tap_countries.singer | target-cratedb --config=settings.json
   

Preview

The README.md can be inspected directly for best reading experience.

Backlog

Probably only happening in subsequent patches after the v0.0.1 release. See also docs/backlog.md.

• Unlock configuring dedicated database schema, not just melty.
  "crate://crate@localhost/?schema=foo"
• Document use with CrateDB Cloud.
• Submit a few patches to meltanolabs-target-postgres, about proper
  quoting of schema and table names.
• Submit a few other patches to crate-python, in order to clean up here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e10e76f) 78.02% compared to head (59dda4e) 78.10%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #3      +/-   ##
==========================================
+ Coverage   78.02%   78.10%   +0.08%     
==========================================
  Files           6        6              
  Lines         546      548       +2     
==========================================
+ Hits          426      428       +2     
  Misses        120      120              

Flag	Coverage Δ
main	78.10% <100.00%> (+0.08%)	⬆️

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