docs: fix img links, closes #2214 (#2282)

docs/introduction/introduction.md

@@ -227,7 +227,7 @@ design their message handlers to create a blockchain that does anything
 useful but this architecture provides a place to start. The diagram
 below illustrates the flow of messages via ABCI.
 
-![](imgs/abci.png)
+![](../imgs/abci.png)
 
 ## A Note on Determinism
 
@@ -263,7 +263,7 @@ Tendermint is an easy-to-understand, mostly asynchronous, BFT consensus
 protocol. The protocol follows a simple state machine that looks like
 this:
 
-![](imgs/consensus_logic.png)
+![](../imgs/consensus_logic.png)
 
 Participants in the protocol are called **validators**; they take turns
 proposing blocks of transactions and voting on them. Blocks are
@@ -329,4 +329,4 @@ The following diagram is Tendermint in a (technical) nutshell. [See here
 for high resolution
 version](https://github.com/mobfoundry/hackatom/blob/master/tminfo.pdf).
 
-![](imgs/tm-transaction-flow.png)
+![](../imgs/tm-transaction-flow.png)