Update issue templates

Author: khannanov-nil

.github/ISSUE_TEMPLATE/new-content-request.md

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+---
+name: New content request
+about: Propose new content to be added to documentation
+title: ''
+labels: documentation
+assignees: khannanov-nil
+
+---
+
+**What is the product for which new content should be added?**
+It can be zkLLVM, Proof Market, zkSharding or Crypto3.
+
+**How should new content fit into documentation?**
+It can be placed in an existing section or form an entirely new section.
+
+**What topic should be covered by new content and what format should it take?**
+Provide a short description such as '*It would be nice to see a tutorial for constructing a zkRollup*' or '*Please add a new code example of EsDSA signature verification in Rust*'
+
+**Why exactly should new content be added?**
+Justify adding new content, see the following examples for reference.
+* '*It is unclear how exactly `assigner` can be extended to support AIR arithmetization, a tutorial series is needed*'
+* '*The community needs to learn more about how the main shard communicates with execution shards in our L2, please add an explanation*'
+* '*I want to use a special build system to build the compiler but the documentation does not contain any instructions for this system. The system is fairly popular so the community will appreciate it if you add this info*'
+
+**Additional context**
+Add any other context here.

.github/ISSUE_TEMPLATE/update-remove-content-request.md

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+---
+name: Update/remove content request
+about: Propose changes to existing content
+title: ''
+labels: documentation
+assignees: khannanov-nil
+
+---
+
+**Where exactly should a change be made?**
+Provide a URL to the page/section where a change in existing content is needed.
+
+**Why should existing content be changed?**
+Justify changing existing content. See the below examples for reference.
+* '*This code example does not compile into a circuit, please change it*'
+* '*This is not the correct flow for procuring a proof via Proof Market*'
+* '*This explanation of zkSharding is too long and complex. The community struggles with understanding it*'
+
+**What would you like to see in place of existing content?**
+Provide a description of how the changed content is supposed to look like and what topics it should cover. See the below examples for reference.
+* '*The reason it doesn't compile is that...So please replace this function with something like this...*'
+* '*The new flow for procuring proofs is this: ...Add it to the docs and expand on it*'
+* '*Remove these terms: ... and make the explanation shorter by one paragraph*'
+
+**Additional context**
+Add any other context about the changes here.