API key permissions mention in USAGE.md

[int-ua]

Fixes #808

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them
• I updated my branch with the master branch
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

I won't spend much time reading all the guides for this small change, feel free to reject this PR and write it in your own words.

[codecov]

Codecov Report

Merging #821 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #821   +/-   ##
=======================================
  Coverage   80.02%   80.02%           
=======================================
  Files          70       70           
  Lines        2018     2018           
  Branches      339      339           
=======================================
  Hits         1615     1615           
  Misses        204      204           
  Partials      199      199

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 610e933...ca962f2. Read the comment docs.

[codecov]

Codecov Report

Merging #821 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #821   +/-   ##
=======================================
  Coverage   80.02%   80.02%           
=======================================
  Files          70       70           
  Lines        2018     2018           
  Branches      339      339           
=======================================
  Hits         1615     1615           
  Misses        204      204           
  Partials      199      199

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 610e933...ca962f2. Read the comment docs.

[codecov]

Codecov Report

Merging #821 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #821   +/-   ##
=======================================
  Coverage   80.02%   80.02%           
=======================================
  Files          70       70           
  Lines        2018     2018           
  Branches      339      339           
=======================================
  Hits         1615     1615           
  Misses        204      204           
  Partials      199      199

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 610e933...c15b316. Read the comment docs.

[thinkingserious]

Hello @int-ua,

Thanks again for the PR!

We want to show our appreciation by sending you some swag. Could you please fill out this form so we can send it to you? Thanks!

Team SendGrid DX