rewrite README

[codecov[bot]]

Codecov Report

Base: 88.74% // Head: 88.74% // No change to project coverage :thumbsup:

Coverage data is based on head (37b0233) compared to base (eb117a9). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #228 +/- ## ======================================= Coverage 88.74% 88.74% ======================================= Files 29 29 Lines 1253 1253 ======================================= Hits 1112 1112 Misses 141 141 ``` | [Impacted Files](https://codecov.io/gh/MattCowgill/readabs/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill) | Coverage Δ | | |---|---|---| | [R/download\_data\_cube.r](https://codecov.io/gh/MattCowgill/readabs/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill#diff-Ui9kb3dubG9hZF9kYXRhX2N1YmUucg==) | `88.23% <ø> (ø)` | | | [R/read\_abs.R](https://codecov.io/gh/MattCowgill/readabs/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill#diff-Ui9yZWFkX2Ficy5S) | `90.90% <ø> (ø)` | | | [R/search\_catalogues.R](https://codecov.io/gh/MattCowgill/readabs/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill#diff-Ui9zZWFyY2hfY2F0YWxvZ3Vlcy5S) | `61.90% <ø> (ø)` | | | [R/show\_available\_catalogues.r](https://codecov.io/gh/MattCowgill/readabs/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill#diff-Ui9zaG93X2F2YWlsYWJsZV9jYXRhbG9ndWVzLnI=) | `91.66% <ø> (ø)` | | | [R/show\_available\_files.r](https://codecov.io/gh/MattCowgill/readabs/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill#diff-Ui9zaG93X2F2YWlsYWJsZV9maWxlcy5y) | `84.78% <ø> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matt+Cowgill)

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