doc: refine PR template

PULL_REQUEST_TEMPLATE.md

@@ -7,12 +7,15 @@
 ## Changelog
 
 ### Enhancements
+
 *Things you added that don't break anything.  Regression tests for Bug Fixes count as Enhancements.*
 
 ### Bug Fixes
+
 *Things you changed that fix bugs.  If a fixes a bug, but in so doing adds a new requirement, removes code, or requires a database reset and reindex, the breaking part of the change should be added to Incompatible Changes below also.*
 
 ### Incompatible Changes
+
 *Things you broke while doing Enhancements and Bug Fixes.  Breaking changes include (1) adding new requirements and (2) removing code.  Renaming counts as (2) because a rename is a removal followed by an add.*
 
 ## Upgrading
@@ -23,7 +26,7 @@
 
 - [ ] If I added new functionality, I added tests covering it.
 - [ ] If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
-  - [ ] I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
+- [ ] I checked whether I should update the docs and did so by submitting a PR to [docs repository](https://github.com/blockscout/docs).
-  - [ ] If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to `master` in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables. 
+- [ ] If I added/changed/removed ENV var, I submitted a PR to [docs repository](https://github.com/blockscout/docs) to update the list of [env vars](https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md) and I updated the version to `master` in the Version column. If I removed variable, I added it to [Deprecated ENV Variables](https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables/deprecated-env-variables/README.md) page. After merging docs PR, changes will be reflected in these [pages](https://docs.blockscout.com/for-developers/information-and-settings/env-variables).
-  - [ ] If I added new DB indices, I checked, that they are not redundant with PGHero or other tools.
+- [ ] If I added new DB indices, I checked, that they are not redundant, with PGHero or other tools.
 - [ ] If I added/removed chain type, I modified the Github CI matrix and PR labels accordingly.