Update broken links in csharp SDK README (#4952)

# Description of Changes

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- Just documentation fixes

# API and ABI breaking changes

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corresponding GitHub label. -->

None

# Expected complexity level and risk

1 - this is just a docs change

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# Testing

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reviewers to do,
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- [x] All links in the README work now.

---------

Signed-off-by: John Detter <4099508+jdetter@users.noreply.github.com>
Co-authored-by: clockwork-labs-bot <clockwork-labs-bot@users.noreply.github.com>

Author: jdetter

sdks/csharp/DEVELOP.md

@@ -4,7 +4,7 @@ We are in the process of moving from the `com.clockworklabs.spacetimedbsdk` repo
 
 # Notes for maintainers
 
-First, see the [user-facing docs](https://spacetimedb.com/docs/sdks/c-sharp).
+First, see the [user-facing docs](https://spacetimedb.com/docs/clients/c-sharp).
 
 ## Developing against a local clone of SpacetimeDB
 When developing against a local clone of SpacetimeDB, you'll need to ensure that the packages here can find an up-to-date version of the BSATN.Codegen and BSATN.Runtime packages from SpacetimeDB.
@@ -64,7 +64,7 @@ Roughly speaking, code pertaining to specific tables should live in `Table.cs`,
 
 ### Threading model
 
-The C# SDK, unlike the [Rust SDK](https://github.com/clockworklabs/SpacetimeDB/tree/master/crates/sdk), **assumes a DbConnection is only accessed from a single thread**. This thread is referred to as the "main thread". The "main thread" is:
+The C# SDK, unlike the [Rust SDK](https://github.com/clockworklabs/SpacetimeDB/tree/master/sdks/rust), **assumes a DbConnection is only accessed from a single thread**. This thread is referred to as the "main thread". The "main thread" is:
 - Whichever thread is repeatedly calling `DbConnection.FrameTick()` in a loop.
 It is **only safe to call `FrameTick()` from a single thread**. It is **only safe to access the DbConnection from this thread**. 
 (Note: we should write about this in the public docs!)