Clarify release instructions

[pnuu]

This PR clarifies the release instructions. The previous version didn't explain which username should be given, and neither did it tell to add the contents of CHANGELOG.temp to CHANGELOG.md before commit. And the version numbers in steps 4. and 5. were 14 minor and 45 patch releases apart.

[codecov]

Codecov Report

Merging #701 into master will increase coverage by 0.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #701      +/-   ##
==========================================
+ Coverage   79.31%   79.68%   +0.36%     
==========================================
  Files         145      145              
  Lines       21120    21191      +71     
==========================================
+ Hits        16752    16886     +134     
+ Misses       4368     4305      -63

Impacted Files	Coverage Δ
satpy/tests/compositor_tests/__init__.py	99.34% <0%> (+0.01%)	⬆️
satpy/tests/reader_tests/test_ahi_hsd.py	97.54% <0%> (+0.48%)	⬆️
satpy/readers/ahi_hsd.py	96.87% <0%> (+22.4%)	⬆️
satpy/composites/cloud_products.py	89.06% <0%> (+36.6%)	⬆️

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[coveralls]

Coverage increased (+0.4%) to 79.685% when pulling af0a04c on pnuu:fix-clarify-releasing into 3e35059 on pytroll:master.

[djhoese]

Love it. Thanks. Had a couple comments and one needed fix.

[djhoese]

I removed the enhancement label since that should probably be limited to code enhancements/features. I'll update the label description now.