Add new policy about airdrop farming

Author: alcuadrado

.github/PULL_REQUEST_TEMPLATE.md

@@ -7,6 +7,15 @@ Please:
  - consider the checklist items below
  - keep the ones that make sense for your PR, and
  - DELETE the items that DON'T make sense for your PR.
+
+## Note about small PRs and airdrop farming
+
+We generally really appreciate external contributions, and strongly encourage meaningful additions and fixes! However, due to a recent increase in small PRs potentially created to farm airdrops, we might need to close a PR without explanation if any of the following apply:
+
+- It is a change of very minor value that still requires additional review time/fixes (e.g. PRs fixing trivial spelling errors that can’t be merged in less than a couple of minutes due to incorrect suggestions)
+- It introduces inconsequential changes (e.g. rewording phrases)
+- The author of the PR does not respond in a timely manner
+- We suspect the Github account of the author was created for airdrop farming
 -->
 
 - [ ] Because this PR includes a **bug fix**, relevant tests have been included.

CONTRIBUTING.md

@@ -139,3 +139,12 @@ When tests are run, Hardhat gets initialized multiple times, and that means unlo
 This problem is normally not present if you are monkey-patching an object that you initialized, but it is when monkey-patching a class, its prototype, or a singleton object initialized by the library itself.
 
 For an example on how to do it properly, please take a look at the `hardhat-truffle5` plugin.
+
+## Note about small PRs and airdrop farming
+
+We generally really appreciate external contributions, and strongly encourage meaningful additions and fixes! However, due to a recent increase in small PRs potentially created to farm airdrops, we might need to close a PR without explanation if any of the following apply:
+
+- It is a change of very minor value that still requires additional review time/fixes (e.g. PRs fixing trivial spelling errors that can’t be merged in less than a couple of minutes due to incorrect suggestions)
+- It introduces inconsequential changes (e.g. rewording phrases)
+- The author of the PR does not respond in a timely manner
+- We suspect the Github account of the author was created for airdrop farming