Further improvements of documentation

[smacker]

From @dpordomingo and @mcuadros comments:

• explain better the features provided by our CLU and GUI #29 (comment),
• assume no context/background in the people reading the README.md #29 (comment), -> Documentation improvements #177
• link to Contributing#Development from our README.md #29 (comment) -> Documentation improvements #177
• clearly document all ENV VARs used for configuration i.e Single binary #36 (comment) → Stop using the odd .env.tpl file #120
• provide information how to run it with DB #170 (comment) → Default env var for CAT_DB_CONNECTION does not work out of the box #173
• update screenshot 😋 -> Documentation improvements #177

or any other not-collapsed comments in the PR #29

[dpordomingo]

All my comments were collapsed (I don't understand why I did wrong :( ); I'll try to list them here.

[bzz]

Added a line to description on ENV VARs.

Update: #120 was created right after

[dpordomingo]

updated issue desc with updates on .env feature

[carlosms]

About this item:

explain better the features provided by our CLU and GUI #29 (comment)

I believe the current readme has a very good introduction. Does anyone have a specific suggestion on how to improve it, or can we mark it as done?

[smacker]

original comment got collapse. So here it is:

@dpordomingo :

With the current wording, I understand the following:

UI to annotate,
CLI to fetch (retrieve/download...) elements and to export.
But current app offers:

GUI UI to annotate and to review the annotations,
CLI to add/push/load fetch new elements to be annotated and to export the annotations made.
@campoy do you think we could reword this section to clarify the features offered by our app?

But for me README is clear in current state.

[bzz]

@carlosms to speed up the review and help understanding the scope that has been addressed - could you please update the checklist in PR description?

[carlosms]

@bzz 👍, main description is now up to date

[smacker]

Guys do you think we still need to document export in readme when we have a link in UI?

[dpordomingo]

I don't think so, it should be moved to other part of our docs (imo same reason as the one for import tool: this project is not focused in import/export databases, but in offering a web interface to annotate code and review code annotations)