Update the README with working test examples

[lbergelson]

Description

• The existing examples of how to run single tests are broken, updating
  them with working examples.
• Closes Gradle : running a single test ? #984

Checklist

• Code compiles correctly
• New tests covering changes and new functionality
• All tests passing
• Extended the README / documentation, if necessary
• Is not backward compatible (breaks binary or source compatibility)

[codecov-io]

Codecov Report

Merging #1225 into master will increase coverage by 0.015%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #1225       +/-   ##
===============================================
+ Coverage     69.016%   69.031%   +0.015%     
- Complexity      8066      8069        +3     
===============================================
  Files            539       539               
  Lines          32552     32552               
  Branches        5488      5488               
===============================================
+ Hits           22466     22471        +5     
+ Misses          7890      7888        -2     
+ Partials        2196      2193        -3

Impacted Files	Coverage Δ	Complexity Δ
...dk/samtools/seekablestream/SeekableHTTPStream.java	58.824% <0%> (+1.471%)	14% <0%> (+1%)	⬆️
...va/htsjdk/samtools/sra/SRAIndexedSequenceFile.java	64.865% <0%> (+2.703%)	7% <0%> (+1%)	⬆️
...samtools/util/AsyncBlockCompressedInputStream.java	76% <0%> (+4%)	13% <0%> (+1%)	⬆️

[lbergelson]

@pshapiro4broad Thank you.

[jmthibault79]

Hooray!