Add --snapshot-pkg-db generation to the README.md

[angerman]

Adding dockets from --snapshot-pkg-db as well; as those might be of interest too.

[nrolland]

I have had pb with snapshot-pkg-db, things like

transformers-compat-0.4.0.4: Found existing documentation. Deleting.
transformers-compat-0.4.0.4 Error: /Users/nrolland/.stack/snapshots/x86_64-osx/lts-5.5/7.10.3/doc/transformers-compat-0.4.0.4/transformers-compat.haddock: openBinaryFile: does not exist (No such file or directory)

except for many libraries. so I trashed my snapshot and recompiled some project using it with stack haddock.

Do you know how to :

• regenerate the documentation if it's missing
• generate the doc for all the packages in a LTS ? at the moment when I compile I only have the package used by my project being added to the snapshot. it would be great to have that done in one shot or better retrieved from some place..

[angerman]

I assume for some reason transformers-compat was built without haddocks, which seems to be more likely a stack bug if, you requested haddocks to be built with stack.

Generating for all of LTS would be great. Though it might be overkill as well, my biggest gripe I have right now, is that even with a slightly larger project, using only the packages from the snapshot database, makes Dash quite slow. I wonder what that would mean for all of LTS.

See also commercialhaskell/stack#491

[nrolland]

for reference this mentions the solution : http://stackoverflow.com/questions/32151623/how-to-add-documentation-after-packages-have-already-been-installed

$ cd $(stack path --snapshot-pkg-db)/../doc
$ stack haddock *

However, those haddock have already been generated on stackage
http://haddock.stackage.org/lts-7.10/

there should be a way to get them automatically and not waste 15 minutes building them but I am unaware of it