Move build instructions to README.md

Move build instructions to README.md

That way, they'll be automatically displayed on gitiles

BUG=
R=andybons@chromium.org, tsepez@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/16703313a78f2370726a0663e9b90d67610daad8

[Tom Sepez, 2015-09-30 19:16:58]

On 2015/09/30 07:53:56, jochen wrote:
Thought this was done in https://codereview.chromium.org/1356323002/

[jochen (gone - plz use gerrit), 2015-09-30 21:07:25]

jochen@chromium.org changed reviewers:
+ andybons@chromium.org

[jochen (gone - plz use gerrit), 2015-09-30 21:07:25]

hum. I guess we should at least update the README then to point to the docs
directory.

i'd still vote for putting the build instructions here instead, because gitiles
only displays the README.me by default

[Tom Sepez, 2015-10-01 16:08:03]

On 2015/09/30 21:07:25, jochen wrote:
> hum. I guess we should at least update the README then to point to the docs
> directory.
> 
> i'd still vote for putting the build instructions here instead, because
gitiles
> only displays the README.me by default
Sounds good.  Can you create a changelist that mv's the location of the existing
files rather than adding them as new?

[jochen (gone - plz use gerrit), 2015-10-02 07:59:38]

done

[Tom Sepez, 2015-10-02 16:33:16]

lgtm

[Bons, 2015-10-05 17:52:25]

lgtm

[jochen (gone - plz use gerrit), 2015-10-07 09:21:07]

Committed patchset #2 (id:20001) manually as
16703313a78f2370726a0663e9b90d67610daad8 (presubmit successful).